Radiographic/fluoroscopic imaging system with reduced patient dose and faster transitions between radiographic and fluoroscopic modes

ABSTRACT

A radiographic/fluoroscopic imaging system provides rapid transition from fluoroscopic to radiographic imaging mode by maintaining the X-ray tube high voltage, increasing the filament current, allowing X-ray tube current to increase toward the desired radiographic current, and terminating exposure when the desired X-ray dose has been achieved. Rapid transition from radiographic to fluoroscopic imaging mode is provided by reducing x-ray tube high voltage to produce an equivalent fluoroscopic-level x-ray output at high initial current, dropping filament current, and enabling ABS control of the high-voltage. As x-ray tube current drops, ABS correspondingly increase high voltage to maintain the desired output. The imaging system obtains movement-related information by analyzing a video signal (such as from fluoroscopic image or an image from an optical camera trained on the patient), or from operator movement requests. The imaging system uses movement-related information to responsively control fluoroscopic pulse rate or other imaging parameters. The imaging system can also use such information to initiate a radiographic exposure, or advance to the next step of an operator programmed examination consisting of interspersed fluoroscopic and radiographic exposures. This results in a lower dose to both the patient and the examiner, consistent with high image quality.

This application is a continuation of Ser. No. 08/753,772 filed Nov. 29,1996.

BACKGROUND OF THE INVENTION

This invention relates to medical diagnostic imaging systems, and moreparticularly, to apparatus and methods for providing highly-versatilediagnostic medical imaging systems capable of performing radiographicand fluoroscopic examinations. Still more particularly, the inventionrelates to radiographic/fluoroscopic imaging systems, and associatedmethods, which achieve rapid transitions between fluoroscopic andradiographic modes, and which employ information regarding detected,forecast, or requested motion of the patient or the imaging system inorder to reduce the x-ray dose delivered to the patient and examiner.

Medical imaging systems capable of performing both fluoroscopic andradiographic examinations have become highly valuable diagnostic toolsin modern radiology. An advantageous application of the dualcapabilities of such imaging systems is peripheral angiography.Peripheral angiography is a diagnostic roentgenographic procedureproviding visualization and recording of the blood vessels in theperipheral region of the body, such as the arms and legs. In a typicalperipheral angiography examination, a radiopaque contrast agent isinjected into a blood vessel, and a rapid sequence of radiographs aretaken to observe the progress of the contrast agent as it flows throughthe vessels along the length of the extremity. The contrast agent isinitially concentrated in the blood vessels and takes some time todiffuse generally into the surrounding regions. Thus, the contrast agentrenders the blood vessels visible under radiography provided that theradiographs are taken very soon after the contrast agent arrives in aparticular region.

In conventional Peripheral Angiography examinations, the patient issupported on a movable table top positioned under system control, Thetable top, in turn, is supported by a stationaryradiographic-fluoroscopic table. An overhead X-ray source (which may bemounted on a tube crane) directs a beam through the patient to a "rapidfilm changer" device.

The locations of interest at any particular time during the examinationare in the general vicinity of the leading edge of the contrast materialas it progresses though the extremity. In conventional peripheralangiography systems, the rapid film changer is normally in a fixedposition. Because the length of the recording radiographic film orimaging device is not sufficient to cover the entire extremity,conventional peripheral angiography systems require that the patient berapidly repositioned throughout the procedure to fully visualize andrecord the contrast material as it progresses through the vessels of theextremity (i.e., the patient must be rapidly repositioned throughout theprocedure to maintain the contrast material within in the field of viewof the rapid film changer). In such conventional systems, the patientrests on a movable table-top, which may travel as rapidly as 9 in/secbetween exposures.

Peripheral angiography is representative of mixedfluoroscopic/radiographic examinations in which the examiner, whileconducting a fluoroscopic examination, desires to immediately perform aradiographic exposure of a feature or event observed on the fluoroscope.For example, when a radio-opaque dye reaches a certain position in thepatient, or some other event of interest occurs during the fluoroscopicexamination, it is desirable to immediately record a high-qualityradiographic exposure for later use.

In conventional equipment of the type heretofore described, a mechanicaloperation is required in order to change from the fluoroscopic mode ofoperation to the radiographic mode, and vice versa. The positions of theradiographic imaging receiver (typically film) or the fluoroscopicimaging receiver (typically an image intensifier) must be exchanged, oran overlapping one of these components must be moved to expose theother. This mechanical operation, even when driven under automaticcontrol of the imaging system, may take one to several seconds. Othertime-consuming activities, such as changing certain X-ray tube operatingparameters, are also required to perform the transition. However, theseactivities generally take less time than the mechanical operation andbecause they are started in parallel, they complete earlier.Accordingly, in older radiographic/fluoroscopic imaging systems, thismechanical operation has been the rate-limiting step controlling thespeed at which transitions between radiographic and fluoroscopic imagingmodes can be achieved.

Recently, however, filmless radiographic/fluoroscopic imaging systemshave been developed which use a single image intensifier (or"photospot") device to receive and record image information during bothfluoroscopic and radiographic exposures. As a result, it is notnecessary to change film between exposures, nor is it necessary toperform other mechanical operations in order to change betweenfluoroscopic to radiographic imaging modes because there is no need:move one component out of the way of another. With the elimination ofmechanical operations, changing the operating current of the X-ray tubehas become the rate-limiting step controlling the speed of transitionsbetween radiographic and fluoroscopic imaging modes in filmlessradiographic/fluoroscopic imaging systems.

For a particular X-ray tube employed in an imaging system, the X-rayoutput delivered by the X-ray tube is directly proportional to the X-raytube current (which is typically measured in milliamperes (mA)), and isapproximately proportional to the fifth power of the X-ray tube voltage(which is typically measured in kilovolts (kV). X-ray tube voltage isselected for the best image contrast, depending on the type of tissuebeing examined and the character of the examination.

In general, fluoroscopic exposures employ relatively low average X-Raytube current (e.g., 0.5-3 mA (average)) over a long exposure time, whileradiographic exposures use high X-Ray tube current (e.g. 100-1000 mA)over a very short time. The X-ray tube cathode operates by thermionicemission. The X-Ray tube current (i.e., the current flowing between theanode and the cathode) is a function of X-Ray tube anode-cathode voltage(or "high voltage"), X-Ray tube cathode (filament) temperature (whichitself is a function of X-Ray tube filament current), and perhaps otherfactors. However, X-Ray tube current (for a particular selected highvoltage) is generally controlled by adjusting the filament temperature,which, in turn, is controlled by adjusting the filament current.

X-Ray tubes which are suitable for both fluoroscopic and radiographicexposures may include one or two filaments of differing sizes. Where asingle filament is used, and it is desired to change from fluoroscopicto radiographic mode, the filament current must be increased to allowthe filament temperature to increase, thereby permitting a higher X-Raytube current which is sufficient for radiographic exposures. Where twofilaments are provided, one filament is typically kept at a standbytemperature just under the cathodic emission temperature, to avoiddeterioration of the filament, except when the filament is selected foruse. Thus, even for two-filament tubes, when a radiographic exposure isdesired, the radiographic filament current must be increased to allowthe filament to heat to a sufficient temperature.

Because it takes time to heat or cool the filament to a desiredtemperature, the X-ray tube current cannot be instantaneouslycontrolled. It typically takes around one second for the filament toheat from an initial temperature (such as its temperature when operatingin fluoroscopic mode or when in standby) to the temperature required fora radiographic exposure. In conventional radiographic/fluoroscopicsystems, the high-voltage power supply to the tube is disabled, therebyinhibiting X-Ray emission, during the filament heating period. Thus, theradiographic exposure does not begin until after the filament reachesthe required temperature. This delay can be significant, because the dyemay progress a substantial distance, or a transient event may haveended, before the radiographic exposure can be recorded.

The opposite transition, from radiographic mode to fluoroscopic mode, isequally important. In radiographic mode, the system operates withrelatively high x-ray tube current. Tube current is a function of thetemperature of the cathode or filament, and therefore, in radiographicmode, the filament must be relatively hot to support the high requiredtube current. In fluoroscopic mode, much lower current, and therefore,accordingly-reduced filament temperature, is typically used. The coolingof the filament is an exponential process over time, so that the tubecurrent cannot be instantaneously reduced to the desired level normallyused for fluoroscopy. In conventional radiographic/fluoroscopic imagingsystems, in which a transition from radiographic to fluoroscopic mode isdesired, the system must wait for the filament to cool down to atemperature appropriate to produce the tube current desired influoroscopic mode. This delay is undesirable.

Another problem with prior art radiographic/fluoroscopic imaging systemsis that they do not optimally minimize the radiation dose delivered tothe patient (and radiologist, technician, or other examining personnel)during an examination. For example, in fluoroscopic examination systems,fluoroscopic exposures may be made continuously, at low X-ray tubecurrent (mA), or in short, repetitive bursts or pulses, at higher tubecurrent. In pulsed fluoroscopy, digital video memory is used to preservethe displayed image between pulses. For a selected average x-ray dose ascontinuous fluoroscopy, the momentary X-ray tube current is higher,resulting in higher signal-to-noise ratio.

Pulsed fluoroscopy systems may have low and high pulse repetition rates.Lower pulse repetition rates are desirable in that they result is alower accumulated radiation dose to the patient, and any other personnelin the vicinity. When an observed scene is stationary, low-rate pulsedfluoroscopy is preferred because it results in a lower dose to thepatient and the operator. However, if movement or changes occur in theobserved scene, the changes appear only when the exposure pulses occur.At low repetition rates, brief transient events may be missed entirely,and movement appears jerky. It has been noted that even inradiographic/fluoroscopic imaging systems which allow the examiner tovary the pulse rate in response to patient motion, examiners often use ahigh pulse rate (appropriate for observing movement) throughout theexamination, including those periods in which no movements or changes inthe image are actually occurring or expected. This undesirably increasesthe radiation dose delivered to both the patient and the examiner.

Nields U.S. Pat. No. 5,119,409 discloses a pulsed fluoroscopy systemwhich analyzes the fluoroscopic image and responsively dynamicallycontrols the fluoroscopic pulse rate based on motion detected in theimage. This system has the disadvantage that the fluoroscopic imagecannot be acquired without exposing the patient to X-rays.

Another disadvantage of prior art radiographic/fluoroscopic systems isthat they employ error-prone methods of determining when to initiate aradiographic exposure. The peripheral angiography examination describedabove is an example of a type of imaging examination to which modernimaging systems are applied in which the patient undergoes a continuousor repetitive-pulse fluoroscopic examination while the examiner awaitsan event of particular interest. The event may be, for example, movementof the patient (as might occur as the patient swallows or breathes), orthe arrival of a contrast medium or dye in the image or at a particularlocation in the image. The occurrence of the event may then trigger thedesire to perform a radiographic examination, which may range from asingle radiographic (or "photospot") exposure to a preprogrammedsequence of radiographic exposures and movement of the patientinterspersed such that the exposures occur at various patient locations.

In prior-art radiographic/fluoroscopic imaging systems, a radiologist ortechnician must observe the fluoroscopic display to detect the event ofinterest, and then initiate the radiographic exposure (and in mostcases, each individual radiographic exposure thereof). This means thatthe observer must have extensive training and experience and must employcareful, vigilant observation. If the radiographic examination isinitiated too early or too late, or the event is missed, the results ofthe examination may be of poor quality or may be entirely useless;re-examination is undesirable because the patient receives additionalexposure to radiation.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aradiographic/fluoroscopic imaging system which avoids the problems anddisadvantages of prior art imaging systems.

It is another object of the present invention to provide a radiographic/fluoroscopic imaging system which achieves rapid transitionsbetween radiographic and fluoroscopic imaging modes.

It is a further object of the present invention to provide aradiographic/fluoroscopic imaging system which provides high imagequality consistent with reduced radiation dose to the patient andexaminer.

It is another object of the present invention to provide aradiographic/fluoroscopic imaging system which employs movement-relatedinformation to control the operation of the imaging system.

It is a further object of the present invention to provide aradiographic/fluoroscopic imaging system which employs movement-relatedinformation to optimally adjust the fluoroscopic pulse rate and otherimaging parameters.

It is another object of the present invention to provide aradiographic/fluoroscopic imaging system which employs movement-relatedinformation to initiate a radiographic exposure upon the occurrence ofan event of interest.

According to an aspect of the present invention, aradiographic/fluoroscopic imaging system provides rapid transitions fromradiographic to fluoroscopic imaging modes, and vice versa. In contrastto prior art systems, when a rapid transition from fluoroscopic toradiographic mode is desired (e.g., an immediate radiographic exposurein the midst of a fluoroscopic examination), the inventive system doesnot disable the x-ray tube high voltage during the filament heatingperiod. Instead, the imaging system performs following steps:

(1) the X-ray tube high voltage (kV) is held constant;

(2) the X-ray filament current is increased to that required forradiography (initiating filament heating to the temperature required tosupport X-ray tube current desired for radiographic exposure;

(3) the radiographic exposure begins immediately, even while the X-raytube current increases in response to increased filament temperature;and

(4) the radiographic exposure is terminated when the desired X-ray dose(effectively, X-ray tube current integrated over time mA·S has beendelivered, using mA·S control or automatic exposure control (AEC).

Thus, although initially the X-ray tube current would be low, it wouldincrease during the exposure, and a substantial fraction of the exposurewould occur during the filament heating period. As a result, theinventive imaging system would allow the resulting radiograph to captureimage information during the filament heating period, which informationwould be missed in prior art systems.

A prior art technique for minimizing total exposure time, but which doesnot achieve the advantages of the invention, is referred to as the"fallen load" technique. The time-vs.-power characteristics of X-raytubes are non-linear. In order to avoid damaging the X-ray tube (e.g. byover-heating the anode), the tube may be operated at maximum power for atiny fraction of time, but may be operated substantially longer or evencontinuously at reduced power. In the "fallen load" technique, totalexposure time is minimized by initially operating the tube at maximumpower for the rated interval. Then the operating power is reducedgradually or in stages, consistent with the tube maximum operating powerspecifications, until an automatic exposure control system indicates adesired total integrated exposure has been achieved. This techniqueoptimally minimizes total exposure time, in contrast to the invention,which optimally provides at least some radiographic exposure as early aspossible.

The inventive imaging system achieves a rapid transition in the oppositedirection, from radiographic to fluoroscopic mode, by exploiting severalknown or empirically-determined relationships between x-ray tubecurrent, x-ray tube high voltage, x-ray tube flux output, and imageintensifier brightness. The X-ray tube flux output is linearlyproportional to x-ray tube current (mA) but is approximatelyproportional to the fifth power of the high voltage (kV⁵). For example,to double the flux output, one may double the x-ray tube current, orincrease the high voltage (kV) by approximately 15 percent. Thus, withinthe operating limits and characteristics of a particular x-ray tube, thesame output or radiation dose (which effectively corresponds to imagebrightness) can be achieved at various selected values of one of thetube operating parameters (tube current or high voltage), provided thatthe opposite parameter (high voltage or tube current, respectively) iscorrespondingly adjusted.

When a radiographic exposure is completed, and it is desired that theimaging system return to fluoroscopic mode, the following steps areperformed:

(1) The small x-ray tube focal spot is selected (if one is available).

(2) Cooling of the x-ray tube filament, which controls current throughthe tube, is initiated by immediately reducing the filament current(c.f. x-ray tube current).

(3) Because the x-ray tube cathode (filament) cannot be instantaneouslycooled, the x-ray tube current is initially that which was used duringthe immediately previous radiographic exposure. The tube current willdecay over time as the filament cools. However, because the x-ray tubeis in operation (i.e., high-voltage is applied), filament cooling isactually much faster than it would be if the tube were idle due todepletion of "hot" electrons from the electron cloud surrounding thefilament.

(4) Ideally, the desired low x-ray tube flux output (or radiation dose)desired for fluoroscopic examination would be produced by operating thetube at a "normal" high voltage and a relatively low x-ray tube current.Because the x-ray tube filament cannot be instantaneously cooled toreduce the tube current to a preferred value, the desired tube output isinstead achieved by immediately reducing the high voltage (which can bealmost instantaneously controlled) to a level which produces the samedesired x-ray tube output at the relatively high initial current. Theimaging system calculates the appropriate x-ray tube high voltage based,in part, on known values of the x-ray tube current and high voltagewhich were used to perform the immediately-previous radiographicexposure.

(5) An automatic brightness system (ABS) is used to control the outputof the X-ray tube during the fluoroscopic examination while the X-raytube filament cools and the X-ray tube current decays to a desired valuefor fluoroscopy. Because x-ray tube output depends on tube current andhigh voltage, as the tube current falls, the high voltage must becorrespondingly increased to achieve constant tube output. ABS is aknown method of automatically adjusting the X-ray tube output to provideconsistent brightness in the image displayed on an image-intensifierscreen. ABS systems typically operate by controlling x-ray tube highvoltage, but may control other parameters. Preferably, the ABS of theinventive imaging system controls x-ray tube high voltage. Thus,throughout the fluoroscopic examination, and in particular while thetube current is changing, the ABS operates to automatically adjust thehigh voltage as required to produce an appropriate tube output forfluoroscopy. Eventually, the x-ray tube filament will have cooled suchthat the tube current reaches the preferred value for fluoroscopicexamination; at that time, the anode voltage will have beenautomatically increased to a "normal" value for fluoroscopy due toaction of the ABS.

According to another aspect of the present invention, the pulserepetition rate used for pulsed fluoroscopy is automatically selected bythe system using movement-related information, such as movement detectedin an x-ray (fluoroscopic) or optical image, operator requests formovement of the patient or imaging system, or knowledge or observationof characteristics of an examination. A low pulse repetition rate may begenerally used. Since the patient under examination is typically restingon a movable table, the movements of which are either controlled by ormonitored by the imaging system, the system may automatically switch toa higher pulse repetition rate whenever the system causes or detects arequest for (or attempt to produce) movement of the patient table orimaging system. In addition, the system may analyze the fluoroscopicimage, or an optical (visible- or infra-red light) image of the patient,or aspects thereof, and automatically switch to a higher pulserepetition rate whenever the image is observed to have changed in asignificant way. For example, the imaging system may switch to a higherpulse repetition rate when it is apparent from the image that motion hasoccurred or a dye or contrast medium has arrived in a window ofinterest. In addition, change in pulse rate may be proportional to therate of movement. Other imaging system parameters may also be changed inresponse to movement-related information.

Automatic control of the fluoroscopic pulse rate makes it substantiallyeasier for the examiner to conduct the examination at the lowest pulserate appropriate for the current examination conditions, therebyresulting in a lower dose to both patient and examiner.

According to another aspect of the invention, methods and apparatus areprovided for automatically detecting motion in a video image acquired bya diagnostic imaging system using x-rays or an optical camera. Themotion detection system is particularly suited to applications inmedical diagnostic imaging.

In first motion detection mode, the full field (i.e. the entire extent)of the acquired image is used for motion detection. The user selects animage variation threshold level. A baseline value for a selectedcharacteristic of the image is initially determined. If the value of theselected characteristic later changes by an amount greater than theuser-selected image variation threshold level, motion detection logicdetermines that motion has occurred.

In a second motion detection mode, a single user-selected window orregion of the display is defined, and motion detection operates onlywith respect to that portion of the image. Motion detection logicoperates as described above to detect motion when a change in the windowexceeding a user-selected threshold occurs.

A third motion detection mode is directed to detect the progress of adye or contrast agent through the image in an expected direction. Firstand second user-selected windows are defined, corresponding to initialand final expected positions of the contrast agent respectively. Motiondetection logic operates as described above to detect initial presenceof the contrast agent when a change in the first window exceeding auser-selected threshold occurs. When the initial presence of thecontrast agent is detected, the imaging system may take certain actionsto improve the diagnostic image and to eliminate motion artifacts. Forexample, the system may increase the fluoroscopic pulse repetition rate,disable frame integration, and enable edge enhancement. The imagingsystem now monitors the second window for a change in the imageexceeding a second user-selected threshold. If a change which exceedsthe threshold is detected, the contrast agent is determined to havereached a final desired position, and a radiographic examination may betriggered. Alternatively, a comparison may be made betweencharacteristics of the two windows to reject common-mode changes in theimage.

According to a further aspect of the invention, the inventive imagingsystem may use movement-related information obtained from theabove-described video motion detector, or from other sources, to controlthe operation of the imaging system. For example, the imaging system mayrespond to movement-related information to initiate a radiographicexposure or advance to the next step of a programmed sequence ofinterspersed radiographic and fluoroscopic exposures.

A "stepping" mode of discretely positioning the imaging system in asequence of radiographic exposures is provided. The system positions theimaging system to a predefined patient location, and initiates afluoroscopic examination. When the system observes that the contrastagent has reached the end of the viewing area, a radiographic exposureis taken, and the system is moved to the next predefined patientlocation.

A "follow" mode of continuously positioning the imaging system is alsoprovided in which the imaging system position follows the contrast agentas it moves through the patient, thereby maintaining the contrast agent(or a detectable mass or leading edge thereof) within the fluoroscopicviewing area. The imaging system makes radiographic exposures atpredetermined positions.

Automatic control of certain imaging system functions based on detectedpatient motion can provide improved examination results because the timerequired to electronically detect the movement and initiate the desiredfunction can be much smaller than that required when observation by ahuman operator is involved. Further, although the attention of a humanoperator may stray, the automatic system remains constantly vigilant,and therefore less likely to miss a movement of interest.

In addition to improving examination quality, the automatic motiondetection may result in the delivery of a reduced total X-ray dose toboth the patient and the examiner. If an event of interest is missed,either the patient must be re-examined, or the patient must beinstructed to perform the movement or event again. In either case,missing the event results in an increased dose. By avoiding missedevents, the automatic motion detection of the present invention canresult in a lower x-ray dose.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be best understood byreference to the following detailed description of a preferredembodiment of the invention, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a partially exploded oblique perspective view showing themechanical structure of a Radiographic/Fluoroscopic diagnostic imagingsystem, which provides an exemplary environment in conjunction withwhich the present invention may be implemented;

FIG. 2 is a block diagram of an exemplary control system for use in theRadiographic/Fluoroscopic diagnostic imaging system of FIG. 1 and inconjunction with which the present invention may be implemented;

FIGS. 3a-3c comprise a flow chart illustrating an exemplary method ofcontrolling the Radiographic/Fluoroscopic diagnostic imaging system ofFIGS. 1-2 in order to provide rapid transitions between radiographic andfluoroscopic imaging modes;

FIGS. 4a-4b comprise a flow chart illustrating an exemplary method ofcontrolling the Radiographic/Fluoroscopic diagnostic imaging system ofFIGS. 1-2 in order to reduce the X-ray dose employed while performingpulsed fluoroscopy examinations;

FIG. 5 is a diagram of an exemplary image display produced by theRadiographic/Fluoroscopic diagnostic imaging system of FIGS. 1-2, inwhich two user-defined windows are provided for detecting movement orchanges in the image, and showing the progress of a contrast mediumthrough the image;

FIGS. 6a-6c comprise a flow chart illustrating an exemplary method ofcontrolling the Radiographic/Fluoroscopic diagnostic imaging system ofFIGS. 1-2 for automatically performing a predefined sequence ofradiographic and fluoroscopic examinations steps in coordination withthe observed movement of contrast medium through a patient;

FIG. 7 is a flow chart illustrating a first exemplary method for usewith the Radiographic/Fluoroscopic diagnostic imaging system of FIGS.1-2 for detecting motion or other changes in a stream of video imageinformation, in which the method may be performed in conjunction withprogrammable processor components of a general-purpose image processor;

FIG. 8 is a block diagram showing the organization of a motion detectionsystem constructed according to the invention for use in detectingmotion or change in a stream of video image information; and

FIG. 9 is a flow chart illustrating a second exemplary method for usewith the Radiographic/Fluoroscopic diagnostic imaging system of FIGS.1-2 for detecting motion or other changes in a stream of video imageinformation, in which the method may be performed in conjunction withthe motion detection system of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment 100 of a Radiographic/Fluoroscopic diagnosticimaging system which provides higher-quality patient examinations,reduced patient dose, and faster transitions between radiographic andfluoroscopic modes, and which is constructed according to the presentinvention is shown generally in FIGS. 1-9. The term "imaging system" asused herein to refer to the invention denotes a versatile suite orcombination of mechanical, electrical, and control components, which arelocated in substantial proximity and which function in a coordinatedfashion to perform a variety of radiographic, fluoroscopic, andoptionally tomographic examinations as selected by an operator.

Because medical imaging equipment requires structural support andgenerates penetrating radiation, in commercial applications it is oftenenclosed in an examination room having sturdy wall, ceiling, and floorstructures constructed of a radiation shielding material, and thisdiscussion of the preferred embodiment of the invention assumes that itwill be applied in such an environment. However, the invention is notlimited to application in this environment, and could be used in otherenvironments (such as a military field hospital) if suitable structuralsupports and radiation shielding are provided.

In addition, although this application describes the present inventionin medical imaging applications in which the images are produced usingX-radiation, it will be appreciated that the present invention may alsobe advantageously used in applications in which images are obtainedusing any suitable type of penetrating radiation, or any other particle,wave, or field phenomenon.

FIG. 1 generally discloses the mechanical configuration of an exemplaryimaging system 100 constructed in accordance with the present invention.FIG. 2 is a block diagram of a control system 510 for coordinating theoperation of the electrical and mechanical components of the imagingsystem 100 of FIG. 1. FIG. 5 is a diagram of an exemplary image displayproduced by the imaging system showing user-defined windows of interestfor automatically detecting motion or changes in the image. FIG. 8 is ablock diagram of a system for automatically detecting movement or changein a stream of image information derived from the imaging system.

FIGS. 3a-3c are flow diagrams showing a method of controlling theimaging system 100 in order to provide rapid transitions betweenradiographic and fluoroscopic imaging modes. FIGS. 4a-4b are flowdiagrams showing a method of controlling the imaging system to reducethe X-ray dose delivered in a pulsed fluoroscopy examination byintelligently adjusting the pulse repetition rate when movement ispredicted, requested, or detected from an image. FIGS. 6a-6c are flowdiagrams showing a method of controlling the imaging system toautomatically perform a predefined sequence of radiographic andfluoroscopic examinations steps in coordination with the observedmovement of contrast medium through a patient.

FIGS. 7 and 9 are flow diagrams showing first and second methods,respectively, for use in conjunction with the imaging system 100 fordetecting motion or other changes in a stream of video imageinformation. The method of FIG. 7 may be performed in conjunction with aprogrammable general-purpose image processor. The method of FIG. 9 maybe performed in conjunction with the motion detection system of FIG. 8.The result from either of the motion detection methods of FIGS. 7 or 9may be used with the methods of FIGS. 4 and 6 to enable the imagingsystem to provide certain automatic operations in coordination with thedetected movement.

The imaging system 100 shown in FIGS. 1-2 and discussed in theaccompanying text forms a highly versatile Radiographic/Fluoroscopicimaging system capable of performing a wide variety of radiographic andfluoroscopic examinations. The present invention is generally directedto methods of controlling an imaging system of this type, but theinvention is not limited to systems having the particular mechanical andcontrol system configurations shown in FIGS. 1-2. Thus, the mechanicalstructure of the imaging system of FIGS. 1-2, and those aspects of itscontrol system which are not directly related to implementing thepresent invention, should be considered an exemplary platform orenvironment in connection with which the present invention may beimplemented. Accordingly, the mechanical structure and control system ofthe exemplary imaging system is discussed herein to the extent relevantto the present invention. However, the imaging system 100 may beimplemented as disclosed in U.S. patent application Ser. No. 08/443,486,filed May 18, 1995, entitled "Universal Radiographic/FluoroscopicDigital Room" (now U.S. Pat. No. 5,636,259), the disclosure of which isincorporated herein.

As best seen in FIG. 1, a preferred embodiment 100 of an imaging systemconstructed according to the present invention may be housed in anexamination room having a floor 130, a ceiling 136, a side wall 132, arear wall 134, and additional walls (not shown), or equivalent supportmembers having sufficient structural strength to bear the weight of thevarious components of the invention.

As best seen in FIG. 1, the imaging system 100 preferably comprisesseveral major functional components: an X-ray tube head 112 supportedfrom the ceiling 136 by a tube crane 110; a floor-mounted examinationtable 116 for supporting a patient (not shown) and an imaging mediacassette 128 (referred to as a "bucky") during examination; a digitalimaging platform 114 supported by table 116; a wall mounted fixture 124for supporting an additional imaging media cassette or bucky 126; anX-ray generator 118; and a main control panel 120 including a controlsystem 510.

Certain of these components are movable in various directions intranslation or rotation as indicated by the motion arrows A--H, andK--L. Some of these movements are performed manually by the operator.Other component movements are mechanically powered. The mechanicallypowered movements may be directed either by an operator (i.e., themovements are "power assisted"), or by the system controller in order toperform a particular imaging examination.

Tube crane assembly 110 supports the X-ray tube head 112 and providestranslational movement of the X-ray tube head 112 in the longitudinal(X) direction shown by arrow A, the transverse (Y) direction shown byarrow L, and the vertical (Z) direction shown by arrow C. The tube craneassembly 110 comprises several cascaded mechanical stages, including atransverse carriage 394, a bridge 144, and a telescoping tube assembly154, each of which permits movement of the X-ray tube head 112 in one ofthe aforementioned directions.

First and second spaced parallel support channels or rails 140 and 142preferably extend longitudinally along the ceiling 136, and are attachedthereto by a plurality of fastening means 148. The support rails 140 and142 support a bridge 144, permitting longitudinal movement of the bridge144 and everything it supports, as shown by the arrow A. The bridge 144,in turn, supports a transverse carriage 394 permitting transversemovement of the bridge and everything it supports, as shown by the arrowL. The transverse carriage 394, in turn supports the X-ray tube head 112by means of a telescoping tube assembly 154 which effectively functionsas a vertically oriented linear bearing. The telescoping tube assembly154 may be formed from a plurality of nested tubular structural members156 having bearings to allow longitudinal slidable movementtherebetween. Thus, the transverse carriage 394 and telescoping tubeassembly 154 permit vertical movement of the X-ray tube head 112, asshown by the arrow C.

Movements along directions A and C are powered by a longitudinal drive150 and a vertical drive 152 respectively. Drives 150, 152 arecontrolled by system controller 510 (FIGS. 1 and 2), and are preferablyhoused in the transverse carriage 394. Movements along directions A andC may also be performed manually by the operator. Transverse movement ofthe tube crane along direction L is not driven, and may only beaccomplished manually by the operator.

The X-ray tube head 112 preferably comprises an X-ray tube headrotational drive (not shown), an X-ray tube assembly 158, an X-raycollimator 164, a control panel 160, and control handles 162 for use bythe operator in selecting the position of the X-ray tube head 112.Information obtained from control panel 160 is preferably communicatedto the system controller 510, which produces control signals to tubecrane longitudinal and vertical drives to move the X-ray tube head 112in the desired direction.

The X-ray tube head 112 is mounted on the telescoping tube assembly 154for rotation about a transverse axis 188 as shown by the arrow B.Projection line 480 depicts the path of X-rays emitted by the X-ray tubehead below collimator 164. Rotation of the X-ray tube head 112 allowsthe X-ray beam to be directed at various desired angles, such as towardthe table 116 (which itself may rotate and translate) or thewall-mounted bucky 126. The X-ray tube head rotational drive (not shown)is controlled by system controller 510.

Thus, the tube crane 110, its associated drives 150 and 152, and theX-ray tube head rotational drive (not shown), cooperate to allow thesystem controller 510 to direct the X-ray tube head 112 to an arbitraryposition on a reference plane parallel to the X-Z plane (within therange of travel provided by the mechanisms of the tube crane), and topoint the emitted X-ray beam at an arbitrary angle along the referenceplane. The transverse position of the reference plane is determined bythe manually adjustable position of the tube crane transverse carriage394, and normally is selected to be coincident with the longitudinalcenterlines of table 116 and wall bucky 126. It is believed thatproviding three degrees of freedom for the position of the focal spotand the angular direction of the emitted X-ray beam, under control ofthe system controller 510, is sufficient for performing examinationsusing a variety of desirable radiographic, fluoroscopic, and tomographicimaging modes. However, a skilled artisan will appreciate that thisembodiment may be easily modified to incorporate additional degrees offreedom if additional imaging modes are desired.

A tiltable patient support table 116 is provided to support a patient(not shown) during examination. The table 116 preferably also supports adigital imaging platform 114 for conducting examinations usingfluoroscopic and stepped techniques. The table 116 preferably comprisesa base 186 for supporting the table and for housing a table tilt drive(not shown). The table tilt drive simultaneously rotates the table abouta transverse axis, as shown by arrow F, and translates the table. Thetranslation is required to modify the effective center of rotation,thereby avoiding interference between the table and the floor. The base184 preferably has a mounting and support plate 184 extendingtransversely to prevent the table from tipping due to the weight of themovable portion of the table, which is cantilevered from the base 184.Table 116 preferably further comprises a table top surface 176 movablein longitudinal and transverse directions as shown by arrows J and K bya 4-way drive system (not shown). The table top drive is controlled bythe system controller 510. The movable table top 176 allows a patient tobe moved to a desired position for examination.

Table 116 preferably further comprises an imaging media cassette or"bucky" 128 disposed in a horizontal shaft 178 below and parallel to thetable top surface 176. The bucky has an interior region (not shown) forreceiving an appropriate imaging medium, such as a piece of radiographicfilm (not shown). The bucky 128 also has a radiographic grid (not shown)for attenuating scattered radiation approaching the imaging medium. Thebucky 128 is movable longitudinally within shaft 178 by a table buckydrive (not shown). Table bucky drive is controlled by the systemcontroller 510. The table 116 may have a control panel 180 to allow theoperator to select the position of the table top 176 and the bucky 180.

A digital imaging platform 114 is provided to perform fluoroscopy,digital image acquisition, and related imaging operations. The digitalimaging platform comprises a support tower 174 extending vertically fromthe table, a support bracket 172 attached to the support tower 174, anX-ray tube assembly 182 disposed below the table top surface 176 andmechanically coupled to the support tower 174, a digital platformcontrol panel 168 attached to the bracket 172, a positioning controlhandle 170, and an image intensifier and camera module 166 attached tothe support bracket and disposed above the table top surface 176. TheX-ray tube 182 and image intensifier module 166 are preferably fixedlymechanically coupled and aligned so that radiation from the X-ray tube182 is directed toward a radiation receiving portion of the imageintensifier module 166. The image intensifier module 166 is provided toconvert received radiation to representative electrical signals 488 forviewing on a monitor 486 or for further processing by other components.

The digital imaging platform 114 is preferably mechanically coupled tothe table 116 using suitable bearing means (not shown) permittinglongitudinal translation of the platform 114 with respect to the table116, as shown by arrow D. An imaging platform longitudinal drive (notshown) is controlled by the control system 510 to direct the imagingplatform to a longitudinal position selected by the operator or, in someimaging modes, by the control system. The control handle 170 preferablyincludes sensors (not shown) for sensing the direction of force appliedto the handle by an operator indicating a desired direction of movementof the platform 114. Information obtained from the sensors is preferablycommunicated to the system controller 510, which produces controlsignals to longitudinal drive to move the platform 114 in the desireddirection.

The inventive imaging system 100 preferably further comprises awall-mounted fixture 124 for supporting an additional imaging mediacassette holder or bucky 126. The fixture 124 preferably comprises avertical support member 190, and an imaging media cassette holder or"bucky" 126 mounted for vertical movement along the vertical supportmember 190, as shown by arrow H. The fixture 124 further comprises means192 for sensing the vertical position of the bucky 126, and a cap member194 disposed at the top of the vertical support 190 for securement to asupport surface and for receiving electrical connections. The bucky 126has an interior region (not shown) for receiving an appropriate imagingmedium, such as a piece of radiographic film (not shown). The bucky 126may have a radiographic grid (not shown) for attenuating scatteredradiation approaching the imaging medium. The fixture 124 is preferablyaligned with the reference plane containing the center line of the table116. The fixture 124 may be secured to the floor 130 using aconventional mounting bracket 198 and suitable fasteners 202, such asbolts. The cap member 194 may be secured to the wall 132 using suitableconventional fasteners 196.

The position of bucky 126 may be manually controlled by the operator,but is not driven. However, the control system 510 receives anelectrical signal 518 indicating the vertical position of the bucky 126as sensed by sensor 192. A skilled artisan will appreciate that thepreferred embodiment may be easily modified to drive wall mounted bucky126 under control of control system 510 if necessary to accomplish adesired imaging mode.

A main control panel 120 interacts with control system 510 to allow theoperator to select operating modes and other functional parameters ofthe inventive imaging system 100. A monitor 486, which may be anysuitable television or computer display, receives electrical signals 488from the image intensifier module 166 or other processing components anddisplays a corresponding image for use by the operator. An X-raygenerator 118 provides electrical power for operating X-ray tubes 158and 182. The X-ray generator converts 118 electrical power from acommercial AC power source to high-voltage DC at a selected voltage, fora selected duration, as instructed by control system 510. The X-raygenerator also supplies power to heat the cathodes of the X-ray tubes158, 182. The X-ray generator 118 preferably regulates the powersupplied to the X-ray tube cathodes to achieve a desired tube operatingcurrent as instructed by the control system 510. A suitable X-raygenerator 118 for use in this application is commercially available fromTrex Medical Corporation, Continental X-Ray Division, 2000 S. 25thAvenue, Broadview, Ill. 60153 (the assignee of the present application),under the name TM Series Generator. Other commercially available X-raygenerators could also be used, by modifying them for compatiblecommunication with control system 510. Although the monitor 486, maincontrol panel 120, and X-ray generator 118 are shown adjacent table 116,they may be remotely located to avoid exposure of the operator toX-rays.

As best seen in FIG. 1, the imaging system 100 incorporates an automaticbrightness system (ABS) 204 and an automatic exposure control (AEC) 206,which are systems well known in the art for optimizing the quality ofimages produced in fluoroscopic and radiographic examinations. The ABS204 is typically used during fluoroscopic examinations and may adjustvarious imaging system parameters in order to maintain the display ofthe image intensifier 166 at a consistent or selected averagebrightness. ABS systems which are known in the art may control suchfactors as X-ray tube high voltage, X-ray tube current, and the gain ofthe image intensifier 166. In the imaging system 100, the ABS 204preferably primarily controls X-ray tube high-voltage to achieve thedesired image intensifier brightness. The AEC 206 is typically usedduring radiographic exposures to terminate the exposure when apreselected integrated x-ray exposure (or dose) has been achieved. TheAEC 206 may determine the exposure by measuring the X-ray dose ratedelivered by the imaging system 100 using an ion chamber or the imageintensifier screen brightness output, and then by integrating that valueover time. The ABS 204 and AEC 206 are depicted in FIG. 1 as separatecomponents coupled to the X-ray generator control 120 and control system510. However, the functions of the ABS 204 and AEC 206 could also beintegrated into the X-ray generator control 120 or another portion ofthe control system 510 so that separate components are not required.

According to one aspect of the present invention, means are provided forobserving the patient optically in the area being examined, fordetecting motion or other changes in the acquired optical image, and forcontrolling the imaging system responsively.

As best seen in FIG. 1, a video camera 408 may be provided for use inobserving an area of the patient's body which is being examined by theimaging system 100. The camera 408 preferably provides a suitable outputsignal 412 which may be used for displaying the image on a monitor (suchas monitor 486). The camera video output signal is preferablysubstantially conformant to a recognized official or industry standardfor video signals so that the signal may be used by conventional displayequipment, video signal processing equipment, and video-to-computersignal conversion equipment. However, cameras providing imageinformation in other forms are available, and one of ordinary skill willappreciate that such cameras could be used in accord with the presentinvention by converting the signal to a standard format, or by modifyingdownstream equipment to accommodate the image information formatprovided by the camera.

Camera 408 is preferably affixed to the digital imaging platform 114such that its field of view is always directed in the general vicinityof the examination region whenever the digital imaging platform is inuse. However, other configurations may also be used. For example,although camera 408 is shown affixed to the digital imaging platform 114in a position facing the patient, the camera could alternately belocated elsewhere, and the optical image could be routed to it using asuitable arrangement of mirrors, prisms, or fiber-optic cables.

Camera 408 is used primarily for observing gross changes in its field ofview. Therefore, any suitable small video camera may be used, includingrelatively inexpensive cameras designed for commercial, industrial, orsurveillance applications. Because room lighting is often minimizedduring examinations, the camera 408 advantageously may be sensitive toboth visible and infra-red light. A lens having a wide-angle of view ispreferred to minimize the need to precisely aim the camera. A camerawhich uses a Charge-Coupled-Device image sensor may be preferred becauseseveral appropriate cameras of that type are readily commerciallyavailable.

The camera output signal 412 is preferably supplied to one or moremotion detection means 406, 496 (FIGS. 2, 8; see also FIGS. 7 and 9).The camera 408, in cooperation with motion detection means 408, 496 andassociated methods, allow the imaging system 100 to perform certainoperations (or steps thereof) automatically, based on movement orchanges observed in the image.

As discussed further in greater detail, image information from camera408 (based on reflected visible or infra-red light) is one of threeprincipal sources of information regarding motion (or other changesaffecting the patient) which the inventive imaging system 100 may use incontrolling its operation. The other two sources are: image informationacquired by the digital imaging platform 114 during fluoroscopy (basedon transmitted X-rays); and commands or requests for movement of thepatient or the imaging system by the examiner. For convenience, we usethe term "movement-related information" to refer to any informationregarding motion (or other changes affecting the patient) originatingfrom these sources. The imaging system 100 may use this movement-relatedinformation in a variety of ways to automate its operation, therebyimproving examination quality and reducing the x-ray dose delivered toboth the patient and the examiner. For example, during a pulsedfluoroscopy examination, the imaging system 100 may automatically adjustthe pulse rate as appropriate when patient motion is detected. In otherexamination modes, the imaging system 100 may automatically switch fromfluoroscopic mode to radiographic mode to make a radiographic exposurewhen motion is detected.

FIG. 2 is a general block diagram of a suitable control system 510 foruse in coordinating the electrical and mechanical components of theinventive imaging system 100 to perform a variety of useful medicalimaging examinations. Several different types of interconnections areprovided between the components of control system 510 of FIG. 2. Thelegends "RS-232" and "RS-422" generally denote point-to-point serialdata links which employ a standardized electrical line discipline. Thelegend "CAN Bus" denotes a serial data link among several interconnectedcomponents. The data is carried over a two-wire party line bus which maysupport a large plurality of independently addressed devices. Althoughfour separate CAN bus links 516, 524, 526, and 540 are shown in thedrawings, those links may be provided over as few as one, or as many asfour, physical CAN busses, depending on traffic requirements. It isbelieved that satisfactory operation of the control system 510 may beobtained using two physical CAN busses. The electrical line disciplineand message protocol of the CAN bus is described in the publication "CANBus Network" from Philips Semiconductor, Microcontroller ProductsDivision. The legend "I/O Port" generally denotes non-serial signalswhich may be analog or digital.

As best seen in FIG. 2, the control system 510 comprises a universalcontrol panel 160, a tomography control module 568, aradiographic/fluoroscopic control module 566, an X-ray generator controlmodule 120, a digital platform control module 554, and a multi-axismotion controller 512.

The universal control panel 160 is located on the X-ray tube head 112,and allows the operator to select, inter alia, the system's examinationmode, and certain operating parameters for radiographic and tomographicexposures. The universal control panel 160 communicates with thetomography control module 568 via a CAN bus link 526 and with theradiographic/fluoroscopic control module 566 via RS-232 link 530.

The tomography control module 568 operates when the imaging system 100is performing a tomographic examination, and also operates any othertime the overhead tube crane 110 is used. The tomography control module568 issues requests to the radiographic/fluoroscopic control module 566and the multi-axis motion controller 512 to drive the tube crane 110,X-ray tube head 112, and table bucky 128 in opposite directions about afulcrum located on the desired tomographic imaging plane of the patient.

The digital platform control 554 communicates with digital platform 114,556 and table 116, 556 via CAN bus 540, and with the digital platformdisplay and control panel 168 via I/O ports 542. Those components, inturn, communicate with the table angulation drive 558 and the table-topsurface four-way drive 560 via I/O ports 536 and 538. Theradiographic/fluoroscopic control module 566 communicates with theuniversal control panel 160 via RS-232 link 530, the X-ray generatorcontrol 120 via RS-232 link 532, the digital platform control 554 via aCAN bus link 524, and the multi-axis controller 512 via can bus links514 and 516. The X-ray generator communicates with the X-ray generatorcontrol using link means 534, which may be implemented using an RS-422link and suitable I/O ports.

In addition, both the multi-axis motion controller 512 and theradiographic/fluoroscopic control module 566 communicate with the tableangulation drive 558 via I/O ports 522, the table top four-way drive 560via I/O ports 520, the wall bucky position sensor 586 via I/O ports 518,the table bucky drive 572, the X-ray tube angulation drive 576, and thetube crane drives 578 and 580 via a CAN bus link 516. In most imagingmodes, the radiographic/fluoroscopic control module 566 transmitsrequests to the multi-access motion controller 512 to control in realtime the movement of each driven component required to perform theexamination. The multi-axis motion controller 512 is capable ofsimultaneous real-time control of motion along up to four axes. Althoughthe multi-axis motion controller 512 can communicate with a largeplurality of client devices, none of the examination modes in which theinventive imaging system 100 is intended to operate require simultaneousmotion in more than four axes. However, the multi-axis motion controller512 may be expanded to simultaneously control additional axes if newimaging modes so require.

The multi-axis motion controller 512 may be any appropriate real-timemotion controller having sufficient throughput and compatible facilitiesfor communicating with the drive systems and with the other controlcomponents of the control system 510. Any suitable commerciallyavailable motion controller capable of controlling simultaneouslymovements along at least four axes may be used. The tomography controlmodule 568, the RF control module 566, the X-ray generator control 120,and the digital platform control 554 may be any implemented using anysuitable control systems of sufficient computing and I/O capacity tocontrol and interface with the required real-world devices. For example,each of these controllers may be constructed using conventionalmicroprocessor and interface technology as is known in the art. Off theshelf general-purpose microcomputer-based control products may be usedto implement these controllers, or each controller may be constructed byselecting only those facilities required to achieve the respectivecontrol functions.

According to an aspect of the present invention, means are provided foranalyzing one or more video (or similar) signals representing optical orX-ray images acquired from the patient and detecting motion or change inthe image over time.

As best seen in FIG. 2, one or more motion detection means 406, 496 maybe provided to analyze video signals (or other similar signals)generated by the video camera 408 and/or the image intensifier 166 todetermine whether motion, or another change of interest, is occurring inan observed image. As discussed previously, the imaging system 100 mayreceive information from three principal sources indicating that motion(or another relevant change in an observed image), is occurring, and mayuse that information to automatically control its operation. Forconvenience, we use the term "movement-related information" to refer toany such information originating from these sources. A first source ofsuch movement-related information is a video signal 412 representing anordinary optical image (i.e., an image resulting from reflected visibleor infra-red light) produced by camera 408 which is trained on theportion of the patient being examined. An advantage of using an ordinaryoptical image of the patient to detect movement is that the imageinformation may be acquired without exposing the patient to examiner tox-rays.

A second source of such movement-related information is a video (orsimilar) signal 414 representing the image acquired by the imageintensifier component 166 of the digital imaging platform 114. The imageinformation from this source results from transmission of x-rays througha portion of the patient undergoing examination. Thus, to acquire imageinformation from the image intensifier 166, the patient must be exposedto x-rays.

A third source of movement-related information is produced fromoperator-actuated movement controls. Most of the movable components ofthe imaging system, including the patient support table 116, are drivenunder the control of the control system 510 at the request of anoperator. Accordingly, whenever the operator requests movement of thepatient or the imaging system, the control system 510 is aware of suchmovement and can respond accordingly. An advantage of using informationregarding movements requested through operator-actuated control is thatit may be acquired without exposing the patient to X-rays. Anotheradvantage of using this source is that it is predictive--i.e.,information about pending movements is acquired before the movementoccurs.

As best seen in FIG. 2, image information signals 412 and 414 producedby camera 408 and image intensifier 166 respectively may be provided toeither or both of first and second motion detection means 406, 496.Since information from the operator-actuated movement controls isacquired directly, it need not be processed by the motion detectionmeans. First and second motion detection means provide similar motiondetection functions, but are implemented differently, and may beconsidered alternatives. Each of the motion detection means 406, 496 areshown with two functional motion detector units or channels, and theboth the image information signal 412 (from camera 408) and imageinformation signal 414 (from image intensifier 166) are shown routed toboth motion detector means 406, 496. However, in a commercial embodimentof the invention, only one of the motion detection means 406, 496 wouldbe implemented, and each of the image information signals would berouted to a respective unit or channel of the motion detection meanswhich was implemented. Each of the motion detection means 406, 496 (oreach independent channel thereof) provides a motion detect output signalon lead or communications path 482 to the digital platform control 554,and may exchange other communications with the digital platform control554 over that path.

Preferably, a motion detection user interface 458 (FIGS. 2, 8) isprovided to allow an operator of the imaging system 100 to select amotion detection threshold and to define regions or "windows" ofinterest for motion detection (e.g. windows 820 and 830; FIG. 5). Themotion detection threshold control allows the user to define the amountof change in an image, over time, which is needed in order to determinethat motion has occurred. The internal operation of the motion detectionmeans 406, 496 is discussed further in detail (see FIGS. 7-9), but insummary, the motion detection means measure the amount of change in theimage over time; if the amount of change exceeds the user-definedthreshold, the motion detection means 406, 496 determines that motionhas occurred, and provides that information to the digital platformcontrol using the motion detection output signal 474. The windowcontrols allow the user to define particular regions or "windows" 820,830 (FIG. 5) of the image to be of interest in motion detection. Forexample, as discussed further in detail, the motion detection means 406,496 may be instructed to respond to movement or change throughout theentire image, or to movement or change within a single window thereof,or to movement or change sequentially affecting two independent windowsthereof.

Each of the motion detection means 406, 496 (or each independent channelthereof) preferably provides a video output signal 488 which may besimilar to the input signal provided to that motion detection means 406,496. The output signal 488 may be supplied to a monitor 486 so that itmay be displayed to the user. The video output signal 488 is preferablykeyed or otherwise modified by the motion detection means to indicatethe user-selected boundaries 812, 814, 816, 818, 822, 824, 826, 828(FIG. 5) of the motion detection windows 820, 830 (FIG. 5) in thedisplayed image 810 (FIG. 5). Techniques for indicating the boundariesare known in the art.

Although the motion detection user interface 458 is depicted as acontrol panel with discrete controls, the user interface 458 could beimplemented using any appropriate control means. For example, the userinterface 458 could also be implemented as functions of one or more ofthe general purpose control panels used to control the imaging system100, such as the main (X-ray generator) control panel 120 (FIGS. 1-2),or the digital platform control panel 168 (FIGS. 1-2). In addition, theuser interface 458 may be implemented using any suitable input andoutput devices, including, for example, analog controls and displays,rotary encoders, conventional computer keyboards and displays, anduncommitted, general purpose, or software-defined controls on a computerbased control panel. The motion detection user interface 458 maycommunicate with each of the motion detection means 406, 496 (or eachindependent channel thereof) using a signal lead (or communicationspath) 474.

First motion detection means 406 may be implemented using one or morestand-alone motion detection modules or circuits for applications of theimaging system 100 in which an accompanying image processing is notprovided. FIG. 8, discussed further in detail, is a block diagram of asingle-channel stand-alone motion detection module or circuit 410constructed according to the present invention. The stand-alone motiondetection module 410 of FIG. 8 may be implemented using any suitabledigital and analog circuitry.

As best seen in FIG. 2, the first motion detection means 406 providestwo independent motion detection channels 410a and 410b, eachimplemented using the circuit 410 of FIG. 8, and each capable ofdetecting motion or relevant changes in a single video signal or streamof video information). However, any desired number of motion detectionchannels may be provided by replicating the circuit 410. FIG. 9,discussed further in greater detail, is a flow diagram illustrating amethod according to the present invention of detecting motion in a videoimage using a stand-alone motion detection module or circuit 410 of thetype shown in FIG. 8.

In some applications, the imaging system 100 is equipped with an imageprocessing system which allows the user to manipulate the imagesproduced by the system in various ways, such as by improving imagecontrast or applying filters or other image operators. Such imageprocessing systems often have high-performance general-purpose orspecial purpose processing units which are capable of performing therequired motion detection function in real-time. Accordingly, secondmotion detection means 496 may be implemented using a suitable imageprocessing system, in conjunction with appropriate motion detectionsoftware or firmware. Several image processing systems are commerciallyavailable which may be used for motion detection, in addition to theimage processing tasks for which image processors are normally appliedin radiology applications. For example, image processors suitable foruse in implementing the second motion detection means 496 arecommercially available from INFIMED Inc., 121 Metropolitan Drive,Liverpool, N.Y. 13088, under the designations "FC 2000" and "QL 2000;"and from CAMTRONICS Ltd., 900 Walnut Ridge Drive, Heartland, Wis. 53029,under the designation "VIDEO PLUS." FIG. 7, discussed further in greaterdetail, is a flow diagram illustrating a method 922 according to thepresent invention of detecting motion in a video image using a typicalcommercially-available image processing system.

As best seen in FIG. 2, the second motion detection means 496 comprisestwo image processing "channels" 490a and 490b. The two channels may, butneed not, correspond to separate physical components. Depending on thecapabilities of the image processor used to implement the motiondetection system 496, a single image processor module (or processingunit) may be capable of performing the motion detection function formultiple video signals; alternatively, a separate processor module orchannel may be required for each video signal to be processed. Althoughthe second motion detection means 496 is shown having two channels formotion detection, any reasonable number of motion detection channelscould be provided by selecting higher performance image processors, orby obtaining additional processors.

Although the internal organization of commercially available imageprocessors may vary, the image processing functions are generallyperformed using digital processing techniques. Each of the imageprocessing channels 490a, 490b is shown with an interface 492a, 492b forconverting video signals 412, 414 received from the camera 408 and imageintensifier 166, respectively, in analog form, into a digital form forsuch processing. However, if one or both of the video signals 412, 414are supplied in digital form, then the corresponding interfaces 492a,492b may be omitted. The motion detection blocks 494a, 494b shown aspart of the image processing channels 490a, 490b correspond to thoseportions of the channels which provide the motion detection functions;the motion detection blocks 494a, 494b may, but need not, correspond toseparate physical components.

According to an aspect of the present invention, means are provided forachieving a rapid transition between radiographic and fluoroscopicimaging modes of the imaging system 100. Radiographic exposures aretypically performed at relatively high X-ray tube currents(approximately 100-1000 mA) over a brief interval. Fluoroscopicexaminations are typically performed at low average X-ray tube current(approximately 0.5 to 3 mA) over long intervals. For a particular X-raytube, at a selected X-ray tube voltage, the X-ray tube current isprimarily determined by the X-ray tube cathode (filament) temperature,which, in turn is controlled by the current flowing through thefilament. When it is desired to operate the X-ray tube at a differentcurrent, it takes time for the cathode to heat or cool to the requiredtemperature. In prior art imaging systems, a substantial delay (ofapproximately one second) has been imposed during the transition betweenfluoroscopic and radiographic imaging modes to allow the cathode toreach the desired temperature. As a result, prior art imaging systemsmay miss some rapidly-occurring events.

In contrast, while the inventive imaging system 100 is performing afluoroscopic examination, the system can initiate a radiographicexposure essentially immediately upon request therefor. When the requestis received, the imaging system 100 uses information which was acquiredby the automatic brightness system (ABS) regarding the fluoroscopicimage brightness during the immediately preceding fluoroscopicexamination to determine the appropriate technique (X-ray tube voltageand current) for the radiographic exposure. The imaging system 100begins the radiographic exposure immediately, setting the X-ray tubevoltage to be used for the radiographic exposure to the voltagepreviously determined by the ABS during fluoroscopy, and setting thefilament current to that needed to ultimately produce the required X-raytube current. Because the X-ray tube cathode is initially at thetemperature used for fluoroscopy, x-ray tube current is also initiallyat the relatively low value used for fluoroscopy but increases thecathode is heated. The exposure is terminated automatically when adesired exposure level, as determined by the mA·S control (when theoperator has selected the "normal" mode), or the AEC 206 (when operatorhas selected the AEC mode), has been reached. As a result of beginningthe radiographic exposure immediately, the imaging system 100 canacquire at least some image information during a rapidly occurringevent, instead of entirely missing the event as might occur when usingprior art imaging systems.

Similarly, if it is desired that the imaging system 100 return to thefluoroscopic examination mode after performing a radiographic exposure,the inventive imaging system 100 can do so immediately, in contrast toprior art systems which have imposed a delay. When the radiographicexposure is completed, the x-ray tube cathode is relatively hot. If theX-ray tube voltage were maintained at the same value used in theradiographic exposure, the high cathode temperature would result inunacceptably high x-ray tube current (and X-ray output) for fluoroscopicexamination. Therefore, using the fluoroscopic technique informationdetermined in the previous fluoroscopic exposure, the imaging system 100determines the correct (lower) X-ray tube voltage required in order toachieve an equivalent X-ray output at the high cathode temperature. Atthe end of the fluoroscopic exposure, the imaging system 100 immediatelyreduces the filament current to initiate cooling of the cathode, lowersthe x-Ray tube voltage, enters the fluoroscopic mode, and enables theautomatic brightness system (ABS) 204. As the filament cools, reducingthe x-ray tube current, the ABS 204 automatically adjusts the x-ray tubevoltage to maintain a consistent brightness on the image intensifierscreen.

FIGS. 3a-3c are a flow diagram illustrating an exemplary method 610according to the present invention for controlling the imaging system100 in order to provide, when appropriate, rapid transitions betweenradiographic and fluoroscopic imaging modes. The functions required toimplement the method 610 are generally provided by the x-ray generator118 (FIG. 1) and the control system 510 (FIG. 2), including the x-raygenerator control 120 (FIGS. 1-2), the ABS 204 (FIG. 1) and the AEC 206(FIG. 2).

The method 610 is invoked at step 612 when the operator selects the"FLUORO-RAD-FLUORO" fast transition option by means of a set-up mode ofthe imaging system 100. Selecting this option enables the imaging system100 to rapidly perform radiographic exposures while in the midst of afluoroscopic examination. Step 614 is the beginning of a primary loop inwhich the system determines, at any particular moment, whether to enterthe radiographic exposure mode, enter the fluoroscopic examination mode,or to await further requests, and whether to attempt a rapid or standardtransition between modes. In step 614, the system determines whether aradiographic exposure is requested. If a radiographic exposure has notbeen requested, the method jumps to step 634, to continue itsdetermination of the requested exposure mode. However, if a radiographicexposure has been requested, the method continues in step 616, in whichthe system determines whether a fluoroscopic examination is in progress.If a fluoroscopic examination is not in progress, the method jumps tostep 622 to begin a sequence of steps for performing a standardradiographic exposure. If a fluoroscopic examination is in progress, themethod continues in step 618, where the system determines whether atwo-factor exposure mode has been selected. In the two-factor exposuremode, the operator sets the x-ray tube voltage and mA.S parameters, andthe imaging system terminates the exposure when the desired mA·S hasbeen reached. If the AEC option is selected, the exposure is similarlyterminated when the desired or dose has been reached.

If a two-factor exposure mode has not been selected (which means thatthe operator has specified a particular X-ray tube current), the imagingsystem 100 cannot perform a rapid transition because the rapidtransition requires varying the X-ray tube current, which then will notcorrespond to the current selected by the operator. Accordingly, themethod jumps to step 622 to begin the standard radiographic exposuresequence. If a two-factor exposure mode has been selected, then themethod continues in step 620, the beginning of the a sequence of stepsresulting in a rapid FLUORO-to-RAD transition. Thus, the requirementsfor performing a FLUORO-to-RAD transition. Thus, in order to perform arapid FLUORO-to-RAD transition, a radiographic exposure must berequested, the system must already be performing a fluoroscopicexposure, and a two-factor exposure mode must have been selected.

In step 620, the system selects the x-ray tube voltage for use in theradiographic exposure to be the same as that determined by the ABS 204during the immediately previous fluoroscopic examination. At step 626,the system determines the required ultimate x-ray tube current usingtechnique information determined by the ABS 204 during the immediatelyprevious fluoroscopic examination. In some applications, an X-ray tubehaving 2 or more filaments, each of a different size and having adifferent maximum emission current rating, may be employed. The smallerfilament provides higher resolution, and is therefore preferred when itcan be used. If the required X-ray tube current exceeds the emissioncapability of the smaller filament, the system selects the largerfilament.

At step 628, the system begins the radiographic exposure immediately,while the filament is heating and the x-ray tube current is rising. Instep 630, the imaging system 100 terminates the radiographic exposurewhen it determines that the preselected value of mA·S has been reached.If the AEC 206 has been enabled, then the imaging system 100 terminatesthe radiographic exposure when it determines that the preselected dosehas been delivered, or the preselected value of mA·S has been reached.If the AEC 206 has been enabled, the mA.S control serves as a backup topreclude delivery of an excessive x-ray dose.

Step 632 represents the end of this sequence, in which a radiographicexposure is performed in conjunction with a rapid transition fromfluorographic mode to radiographic mode. In step 634, the imaging systemdetermines whether the operator has requested that the system return tothe fluoroscopic examination mode once the radiographic exposure iscompleted. If the "FLUORO" mode was not requested, the method loops backto step 614, whereupon the primary mode-determination loop is restarted.

However, if in step 634, the "FLUORO" mode was selected, the methodcontinues with step 636, in which the system selects small focal spot ofthe X-ray tube for use. The small focal spot is preferred whenever thex-ray tube current is low enough to permit its use because it provideshigher resolution. The focal spot is the projection of the filament onthe image plane. Hence, selecting the small focal spot is equivalent toselecting the small filament.

In step 644, the system determines whether the ABS 204 is enabled. Ifthe ABS 204 is enabled, then the method continues with step 646, whichis the first in a sequence of steps for performing a fast transitionfrom radiographic to fluoroscopic mode. At the termination of theradiographic exposure, the x-ray tube cathode is at the high temperaturerequired to supply the relatively-high x-ray tube current required forradiography, and it cannot be instantaneously cooled.

For a particular combination of X-ray tube, and filament the x-ray tuberadiation output is directly proportional to the x-ray tube current, andapproximately proportional to the fifth power of the x-ray tube highvoltage. When the imaging system returns to fluoroscopic mode, it isdesirable to provide the same image-intensifier brightness as waspreviously used during fluoroscopy, and therefore, it is desirable toprovide the same fluoroscopic mode x-ray tube output as was previouslyused. Although the x-ray tube current cannot be instantaneouslycontrolled, the X-ray tube voltage can be (within a few milliseconds).Therefore, when a fast transition from radiographic to fluoroscopic modeis to be performed, the imaging system determines an initial X-ray tubevoltage which is required, when the tube is operated at the initiallyhigher current, to cause the tube to produce the desired fluoroscopicmode x-ray output. This initial voltage is always lower than the voltageused during the radiographic exposure.

As the x-ray tube filament cools, the x-ray tube current drops, and thex-ray tube voltage must be correspondingly increased to maintain aconsistent x-ray output and image intensifier brightness. This functionis automatically performed by the ABS 204. Thus, if the ABS 204 is notenabled, the desired x-ray output cannot be maintained, and the imagingsystem 100 cannot perform a rapid transition. In that case, the methodcontinues with step 660, which is the first in a sequence of steps forperforming a normal transition from radiographic to fluoroscopic mode.

If ABS is enabled, the rapid RAD-to-FLUORO transition sequence beginningwith step 646 is performed. In step 646, the imaging system 100determines the initial x-ray tube voltage required to cause the tube toproduce the desired fluoroscopic mode x-ray output when operated at theinitially high current (resulting from the filament being at the hightemperature required for the radiographic exposure). The desired outputis typically the same as was used during fluoroscopy immediately priorto the radiographic exposure, so that the image intensifier brightnesswill be the same. The initial x-ray tube voltage will be lower than thevoltage used during the just-completed radiographic exposure.

In step 648, the fluoroscopic examination is started immediately, usingthe initially high x-ray tube current, and the initially lowered x-raytube voltage. The filament current is reduced to allow the cathode tocool, which, in turn, causes a reduction in the x-ray tube current. Inaddition, when the X-ray tube is operating (i.e., high voltage isapplied), the filament cools much faster than when the X-ray tube is inan idle condition. Thus, the rapid RAD-to-FLUORO transition of thepresent invention causes the X-ray tube current to return to a valueappropriate for fluoroscopy more rapidly than would otherwise beaccomplished. In step 650, as the filament cools, the x-ray tube currentfalls, the ABS correspondingly increases the x-ray tube voltage tomaintain constant image intensifier brightness (and, effectively,constant x-ray tube output). Eventually, the x-ray tube current falls,and the x-ray tube voltage rises, to their normal fluoroscopic levels.

Step 652 represents the end of this sequence, in which a rapidtransition from radiographic mode to fluoroscopic mode has beenperformed. In step 654, the fluoroscopic examination continues under thesupervision of the ABS 204, which maintains a constant brightness on thedisplay of the image intensifier 166. In step 656, the imaging systemdetermines whether the fluoroscopic examination is still in progress, orhas been terminated by the operator. If the examination has beenterminated, the method loops back to step 614, whereupon the primarymode-determination loop is restarted. Otherwise, the method returns tostep 654, and the loop consisting of steps 654 and 656 are performeduntil the examination is terminated.

If, in step 644, the imaging system determined that the ABS 204 was notenabled, the method continues at with step 660, which is the first in asequence of steps for performing a normal transition from radiographicto fluoroscopic mode. In step 660, the imaging system sets the x-raytube voltage and current to operator-selected values. The x-ray tubecurrent is primarily determined by the cathode temperature, which, inturn, is controlled by the filament current. Accordingly, the systemsets the filament current to that required to produce the desired x-raytube current, but it takes some time for the cathode to cool to thedesired temperature. In step 662, the imaging system 100 determineswhether the cathode has cooled to the desired temperature. If thecathode is still too hot, step 670 is performed, in which the systemdelays for a predetermined interval to allow the cathode to cool, andthen the method loops back to step 662. The loop consisting of steps 670and 662 is performed until the filament reaches the desired temperature.Once the filament is ready for use, step 664 is performed, in which thefluoroscopic examination is initiated using the operator-selectedtechnique.

Step 666 represents the end of this sequence, in which a normaltransition from radiographic mode to fluoroscopic mode has beenperformed. In step 668, the imaging system determines whether thefluoroscopic examination is still in progress, or has been terminated bythe operator. If the examination has been terminated, the method loopsback to step 614, whereupon the primary mode-determination loop isrestarted. Otherwise, the method returns to step 668, and thefluoroscopic examination continues until terminated by the operator.

If, in steps 614-618, the system determined that a radiographic exposurewas requested, but a rapid transition to radiographic mode could not beperformed, the method jumps to step 622 to begin a sequence of steps forperforming a standard radiographic exposure. In step 622, the imagingsystem 100 sets the x-ray tube voltage to a value selected by theoperator. In step 624, if the x-ray tube includes multiple filaments,the imaging system selects the filament appropriate for theoperator-selected x-ray tube current. In step 638, the system sets thex-ray tube current to a value selected by the operator. In step 640, thesystem supplies filament current to the x-ray tube and waits until thefilament reaches the proper temperature to produce the operator-selectedx-ray tube current. Then the system performs a normal radiographicexposure using the operator-selected technique.

Step 642 represents the end of this sequence, in which a radiographicexposure is performed in conjunction with a normal transitionradiographic mode. The method loops back to step 614, whereupon theprimary mode-determination loop is restarted.

As disclosed above in connection with FIGS. 1-2, the imaging system 100may receive information from several sources indicating that motion (oranother relevant change detected in an optical or x-ray image acquiredfrom the patient), is occurring, and may use that information toautomatically control its operation. According to an aspect of thepresent invention, the imaging system 100 may use movement-relatedinformation to advantageously reduce the x-ray dose received by thepatient and the examiner during a pulsed fluoroscopy examination, whilecontinuing to provide high-quality images, even when motion isoccurring.

The term "pulse" refers to a short burst of x-rays emitted at regularintervals to enable a fluoroscopic image to be acquired. Pulsedfluoroscopy may be preferred over continuous fluoroscopy in someapplications because the individual x-ray pulses may be emitted at ahigher instantaneous dose rate while still maintaining a very lowaverage dose rate. Images acquired at higher instantaneous dose ratesgenerally exhibit improved signal-to-noise ratio.

Although pulsed fluoroscopy systems providing several user-selectablepulse rates are known, examiners do not always select the optimum pulserepetition rate during all phases of an examination. It is generallydesirable to use a higher pulse repetition rate whenever relative motionbetween the patient and the imaging system occurs (or is expected tooccur), or whenever an event causing a change in the image occurs or isexpected. A higher pulse rate eliminates or reduces the "jerky"appearance of motion. However, when no motion or change in the image isexpected, a lower pulse repetition rate is strongly preferred because itresults in a substantially lower dose to both the patient the examiner.Despite the availability in prior art imaging systems of a range ofselectable pulse repetition rates, it has been observed that examinersoften will operate the systems at one of the higher rates throughout thefluoroscopy examination, even during periods when no movement or changein the image is expected.

FIGS. 4a-4b are a flow diagram illustrating an exemplary method 710according to the present invention for controlling the imaging system100 in response to movement-related information in order to responsivelyselect the fluoroscopic pulse rate and other imaging system parameters.The functions required to implement the method 710 are generallyprovided by the control system 510 (FIG. 2), x-ray generator 118(FIG. 1) and the x-ray generator control 120 (FIGS. 1-2).

The method 710 begins in step 712. In step 714, the control system 510prepares to use an initial fluoroscopic pulse rate during portions ofthe examination in which no movement or other significant change isexpected in the acquired fluoroscopic image. Preferably, the imagingsystem 100 is capable of providing a plurality of pulse ratesappropriate for fluoroscopic examinations ranging from high pulse ratessuitable for smoothly reproducing motion, to low rates suitable forobserving an essentially static image. For example, the imaging systemmay provide selectable pulse rates of approximately 30, 15, 7.5, 3.8,and 1.9 pulses per second (PPS). The 30 PPS rate is approximately equalto the frame repetition rate used in television systems and isconsidered suitable for observing full-speed motion. Other rates mayalso be provided. As is known in the art, the imaging systemfluoroscopic display preferably comprises suitable image memory (notshown) so that the most recently acquired image is continuouslydisplayed between pulses. The "initial" pulse rate established in step714 is preferably selected by the user from the lower end of the rangeof available rates, to minimize the dose to which the patient andexaminer are exposed when no movement is expected.

In step 716, the control system 510 prepares to use an initial frameintegration rate during portions of the examination in which no movementor other significant change is expected in the acquired fluoroscopicimage. The step is optional and may be omitted if the frame integrationmeans is not available or if the examiner elects not to use it. Frameintegration is a known method of reducing noise and minimizing artifactsin essentially static images by accumulating and displaying imageinformation from multiple views or "frames" of the same image acquiredover time. Each time a fluoroscopic pulse is emitted, the resultantacquired image is stored as a frame of image information. By effectivelyaveraging the value of each pixel over multiple acquisitions, frameintegration reduces the effect of transient changes in the image, suchas image noise. The frame integration rate refers to the number ofprevious frames of image information used in displaying the presentinformation. Preferably, a plurality of selectable rates may beprovided. In a commercial embodiment of the imaging system 100, forexample, rates of 1, 2, 4, 8, and 16 may be selected. Higher ratesimprove noise reduction in static images, but increase artifacts inmoving images, because image features are shown at multiple (old)locations. The "initial" frame integration rate established in step 716is preferably selected by the user from the higher end of the range ofavailable rates, to maximize noise reduction when no movement isexpected.

In step 718, the control prepares to use an initial edge enhancementlevel during portions of the examination in which no movement or othersignificant change is expected in the acquired fluoroscopic image. Thestep is optional and may be omitted if the edge enhancement means is notavailable or if the examiner elects not to use it. Edge enhancement is aknown method of improving the visibility of image features which mayrepresent the edges of structures. Higher edge enhancement levels may bepreferred for observing moving images. When observing static images,less or no edge enhancement may be needed. The "initial" edgeenhancement level established in step 718 is preferably selected by theuser from the lower end of the available rates.

Step 720 is the first step of a primary loop in which the control system510 waits for a fluoroscopic examination to start, waits for anindication of movement or a significant change in an image acquired fromthe patient, and if such indication is received, responsively adjuststhe parameters of the fluoroscopic examination to those suitable forobserving the moving or changing fluoroscopic image.

In step 720, the control system 510 determines whether the fluoroscopicexamination is in progress. If the fluoroscopic examination is not inprogress, then the control system 510 need not alter examinationparameters in response to motion, and the method loops back to step 720until the examination begins. Also in step 720, whenever a fluoroscopicexamination begins, the control system 510 causes operation at a highfluoroscopic pulse rate for a brief interval in order to stabilize theoperation of the image intensifier 166 and the automatic brightnesssystem (ABS) 204. For example, the system may operate at the 30 PPS ratefor a stabilization period 8 pulses, in order to rapidly stabilize theimage intensifier 166 and the ABS 204. Once the stabilization period iscomplete, the fluoroscopic pulse rate is maintained at the slowerinitial rate.

In step 722, the control system 510 determines whether the operator hasrequested movement of the digital imaging platform 114 (also referred toas the "fluoro carriage"). In step 724, the control system 510determines whether the operator has requested movement of the patientsupport table 116. The imaging system 100 provides driven motion of thedigital imaging platform 114 and the patient support table 116 inresponse to operator requests therefor. The operator communicates theserequests using motion control switches and handles located on thedigital imaging platform control panel 168, digital imaging platformpositioning control handle 170, and patient support table control panel.180. The control switches are operatively connected to the controlsystem 510. Thus, whenever the operator requests movement of the digitalimaging platform 114 or the table 116, the control system 510 is awareof the request. If, in steps 722 or 724, a movement request wasdetected, the method jumps to step 730. If no movement was detected, themethod continues at step 726.

In step 726, the control system determines whether motion, or anotherrelevant change, has been detected in the fluoroscopic image beingacquired in the examination, or the optical image of the examinationregion. Either or both of the video images from the image intensifier166 and the optical camera 408 may be analyzed by motion detection means406, 496 (FIG. 2; see also FIGS. 7-9). If motion or other image changeswas detected, the method jumps to step 730. If no motion was detected,the method continues with step 728. In step 728, if the examinationparameters were changed, the control system resets these parameters totheir initial values. The imaging system continues the fluoroscopicexamination using the initial parameters. Then method returns to step720 to re-execute the primary loop.

In steps 730-736, the control system modifies the fluoroscopicexamination parameters in response to the motion determined in steps722-726. In step 730, the control system 510 determines the rate ofmotion which was requested or detected. For imaging system movementrequested by the operator, the control system 510 has definitiveinformation as to the rate of that motion. For motion detected in avideo signal, the motion detection means may determine the rate at whichthe leading edge of a moving feature advances on a pixel-by-pixel basisusing well-known methods.

In step 732, the control system proportionally increases thefluoroscopic pulse rate to a rate appropriate for observing thefluoroscopic image in which motion is occurring at the determined rate.Preferably, the control system 510 selects a faster fluoroscopic pulserate when the determined rate of motion is greater, in order to provideimproved image quality.

In step 734, the control system proportionally reduces the frameintegration rate (if frame integration is enabled) to a rate appropriatefor observing the fluoroscopic image in which motion is occurring at thedetermined rate. Preferably, the control system 510 selects a lowerframe integration rate when the determined rate of motion is greater, inorder to provide improved image quality.

In step 736, the control system proportionally increases the edgeenhancement level (if edge enhancement is enabled) to a levelappropriate for observing the fluoroscopic image in which motion isoccurring at the determined rate. Preferably, the control system 510selects a higher edge enhancement level when the determined rate ofmotion is greater, in order to provide improved image quality.

In some applications, it may not be desirable or necessary to modify thefluoroscopic pulse rate, frame integration rate, and edge enhancementlevel proportionally. In such applications, step 730 may be omitted, andsteps 732, 734, and 736 may modify the fluoroscopic pulse rate, frameintegration rate, and edge enhancement level, to respectiveuser-selected values for use when motion is present. Step 730, and the"proportional" features of 732, 734, and 736 are shown in broken linesto indicate that proportional adjustment of these parameters isoptional.

In steps 738-742, the control system 510 determines whether to return tostep 728 to reset the fluoroscopic examination parameters to theirinitial values. In step 738, the control system 510 determines whetherthe fluoroscopic examination is still in progress. If the examination isnot still in progress (i.e., if the operator has terminated theexamination), the method jumps to step 728. Otherwise, in step 740, thecontrol system 510 determines whether motion of the digital imagingplatform 114 was the reason for using the motion-specific parameters,and if so, whether the motion has been de-selected. If both of thoseconditions are true, then is it no longer necessary to use themotion-specific fluoroscopic examination parameters, and therefore, themethod jumps to step 728 to reset them to their initial values.Otherwise, the method continues at step 742.

In step 742, the control system 510 determines whether motion of thepatient support table 116 motion of the patient support table 116 wasthe reason for using the motion-specific parameters, and if so, whetherthe motion has been de-selected. If both conditions are true, then is itno longer necessary to use the motion-specific fluoroscopic examinationparameters, and therefore, the method jumps to step 728 to reset them totheir initial values. Otherwise, the method loops back to step 738 tocontinue the fluoroscopic examination using the motion-specificparameters.

Whenever the method reaches step 728, the control system resets thefluoroscopic examination parameters to their initial values, and returnsto the beginning step 720 of the primary loop. If the examination isstill in progress, then the control system executes the loop repeatedlyuntil motion is again detected. If the examination is not still inprogress, then the control system waits at step 720 until an examinationbegins.

The method 710 allows the imaging system 100 to perform fluoroscopicexaminations at low fluoroscopic pulse rates except when motion isdetected or requested, at which time the imaging system automaticallyuses a higher pulse rate. This advantageously reduces the dose deliveredto the patient and examiner, while providing high image quality whenmotion or image change occurs. It also minimizes inconvenience to theexaminer by eliminating the need to manually change the pulse rates asthe examination progresses from phase to phase, and eliminates theincentive to the examiner to operate the system at a high pulse ratethroughout the examination. Although the method describes changingseveral specific fluoroscopic imaging parameters in response torequested (forecast) or detected motion, any other parameters controlledby control system 510 could also be responsively controlled.

Automatic control of certain imaging system functions based on detectedor forecast patient motion can provide improved examination resultsbecause the time required to electronically detect the movement andinitiate the desired function can be much smaller than that requiredwhen observation by a human operator is involved. Further, although theattention of a human operator stray, the automatic system remainsconstantly vigilant, and therefore less likely to miss an movement ofinterest.

In addition to improving examination quality, the automatic motiondetection may result in the delivery of a reduced total X-ray dose toboth the patient and the examiner. If an event of interest is missed,either the patient must be re-examined, or the patient must beinstructed to perform the movement or event again. In either case,missing the event results in an increased dose. By avoiding missedevents, the automatic motion detection of the present invention canresult in a lower x-ray dose.

According to a further aspect of the present invention, the imagingsystem 100 may use the movement-related information to control theprogress of a preprogrammed radiographic/fluoroscopic examination inwhich coordinated movement of the patient and/or the imaging system iscarried out simultaneous with or interspersed among radiographic and/orfluoroscopic exposures.

FIG. 5 is a diagram showing schematically an exemplary image display 810produced by the imaging system 100 in an examination in which theprogress of a radio-opaque die or contrast medium 832 progresses througha portion of a patient's body subject to examination. This procedure isused in various imaging system applications. For example, in peripheralangiography examinations, the contrast medium is injected into thepatient's blood stream. The progress of the contrast medium is observedfluoroscopically as it moves through the patient's circulatory system.The contrast medium enhances the radiographic appearance of thecirculatory vessels. In order to create a radiographic record of thestructure of the patient's circulatory system, it is desired to make acomplete series of radiographic exposures as the contrast mediumprogresses through various locations.

To minimize the dose to which the patient is exposed, it is preferredthat the exposure locations be selected such that the exposures producecomplete, but minimally overlapping coverage. In order to accomplishthis, the imaging system components must be precisely moved to thedesired locations, and the exposures must be initiated, in coordinationwith the movement of the contrast medium. In prior art systems, thiscoordination was performed by predicting the rate of contrast mediumprogression and scheduling the exposures at particular times, or byhaving an examiner observe the progression of the contrast medium in thefluoroscopic image and command the radiographic exposure when thecontrast medium is observed to have reached the desired location. In thepast, such coordination has often proved imperfect, with the resultsthat: examination quality has been degraded; excessive overlappingexposures, or complete reexaminations have been required; and the doseto the patient has been higher than desired.

FIGS. 6a-6c comprise a flow chart illustrating an exemplary method 840of controlling the imaging system 100 automatically performing apredefined sequence of radiographic and fluoroscopic examinations stepsin coordination with the observed movement of contrast medium through apatient. The method 840 will be discussed in connection with FIG. 5.

The method 840 begins in step 842. In step 846, the control system 510prepares to use an initial fluoroscopic pulse rate during portions ofthe examination in which no movement or other significant change isexpected in the acquired fluoroscopic image. The "initial" pulse rateestablished in step 846 is preferably selected by the user from thelower end of the range of available rates. As shown in result block 844,this minimizes the dose to which the patient and examiner are exposed.

In step 850, the control system 510 prepares to use an initial frameintegration rate during portions of the examination in which no movementor other significant change is expected in the acquired fluoroscopicimage. The step is optional and may be omitted if the frame integrationmeans is not available or if the examiner elects not to use it. The"initial" frame integration rate established in step 850 is preferablyselected by the user from the higher end of the range of availablerates, to maximize noise reduction when no movement is expected.

In step 852, the control system 510 prepares to use an initial edgeenhancement level during portions of the examination in which nomovement or other significant change is expected in the acquiredfluoroscopic image. The step is optional and may be omitted if the edgeenhancement means is not available or if the examiner elects not to useit. The "initial" edge enhancement level established in step 852 ispreferably selected by the user from the lower end of the availablerates. Block 848 indicates that the result of steps 850, 852 is improvedimage quality.

In step 854, the user selects the "auto center" option, which enables anexamination mode in which the imaging system 100 performs a series ofradiographic exposures at pre-planned locations with respect to thepatient. The imaging system 100 and its control system 510 managesmovement of the digital imaging platform 114 and the patient supporttable 116, and coordinates radiographic and fluoroscopic exposuresaccording to instructions programmed by the operator in step 854.

In step 856, the user employs the motion detection user interface 458(FIGS. 2, 8) to select the size and positions of the windows of interest820, 830 (FIG. 5). Windows 820, 830 define the portions of thefluoroscopic image 810 which will be analyzed for movement or othersignificant change by the motion detection means 806, 896. The user mayelect to use one, two, or more windows. For example, the operator mayelect to use one window per leg, in an examination of both legs, for atotal of four windows. When operating in the one-window mode, theimaging system 100 moves to a user-programmed location, and awaits amovement indication. As the contrast agent progresses through location832a to location 832b, the arrival of the contrast agent in the windowis detected by the motion detection means 806, 896 as a change in thebrightness of the image within the window (see FIGS. 7-9). When themotion detection means 806, 896 indicates that motion or change has beenobserved, the imaging system performs the user-programmed radiographicexposure; the imaging system then advances to the location associatedwith the next programmed step and again awaits the detection of thecontrast medium.

When operating in the two-window mode, the imaging system 100 usesmotion detected in the first defined window 820 at location 832b as atrigger to initiate operation using the motion-specific fluoroscopicparameters (i.e., higher pulse rate, lower frame integration, higheredge enhancement). As the contrast medium progresses to location 832c,the imaging system waits. When the contrast medium progresses tolocation 832d, motion or change is detected in the second defined window830, and the imaging system performs the programmed radiographicexposure step. As the contrast medium progresses to location 832e, theimaging system moves to the location of the next user-programmedexamination step. When the operator elects to use more than two windows,a similar method is used.

In step 860, the user employs the motion detection user interface 458(FIGS. 2, 8) to select an image variation threshold for use by themotion detection means 806, 896. The motion detection means 806, 896monitors the changes in brightness (or another parameter) of an inputimage signal within the user selected windows. If the changes exceed theimage variation threshold selected by the user, the motion detectionmeans 806, 896 interpret such changes as motion and provide anindication that motion is detected to the control system 510.

In step 862, the user may select whether the imaging system operates in"Stepping" or "Follow" mode. The "Stepping" mode employs discretepositioning of the imaging system. For each predefined step (describedabove in connection with step 856), fluoroscopy is used to observe theprogress of the contrast medium to the end of the viewing area, and aradiographic exposure is made. The system then moves to the next stepposition. The "Follow" mode employs continuous positioning of theimaging system. Fluoroscopy is used to observe the progress of thecontrast medium, and the imaging system is continuously positioned tomaintain the contrast medium within the viewing area. When the imagingsystem reaches certain user-programmed locations, radiographic exposuresare made.

In step 864, the control system 510 determines whether the operator hasrequested the fluoroscopic examination to begin. If not, the methodloops back to step 846 and repeats. If the operator has requestedfluoroscopic examination to begin, the method continues in step 866, inwhich the control system commences the fluoroscopic exposure. In step868, the control system waits until the ABS 204 reaches a stableoperating condition. At step 872 the control system records andmaintains the x-ray tube voltage level, effectively disabling the ABS204. This step is required because otherwise the ABS 204 would seek tomaintain a consistent image brightness as the contrast medium arrives,thereby defeating the motion detection means 806, 896. See result block870.

In step 874, the motion detection means 806, 896 determines whether anyvariation in the image which have occurred in window 1 820 exceeds thethreshold selected by the user in step 860. The system waits until theimage variation exceeds the threshold, and then progress to step 876, inwhich the motion detection means 806, 896 provides an indication thatmotion has been detected in window 1 820. See result block 878.

In step 880, the system determines whether the operator has selected theone-window mode or the two-window mode. If the operator has selected theone-window mode, the motion detection signal means that the contrastmedium has appeared in the area of interest. Therefore, the methodcontinues at step 884, which is the beginning of a sequence of steps inwhich the system performs the operator-programmed radiographic exposureand moves to a next desired examination location.

If the operator has selected the two-window mode, the motion detectionsignal means that the contrast medium is present in the image, but theimaging system must wait until the contrast medium has reached the areaof interest (i.e., the end of the viewing area) before performing theradiographic exposure. The method continues at step 902. In steps 902,904, and 906, the control system 510 changes the fluoroscopicexamination parameters to those suited for observing motion (see steps730-736, FIG. 4b). In step 902, the control system increases thefluoroscopic pulse rate. In step 904, the control system reduces or theframe integration rate (or eliminates frame integration altogether). Instep 906, the control system enables or increases the edge enhancementlevel. As shown by result block 898 and 908, steps 902, 904, and 906improve the quality of the diagnostic image, and eliminate motionartifacts.

In step 910, the motion detection means 806, 896 determines whether anyvariation in the image which have occurred in window 2 830 exceeds thethreshold selected by the user in step 860. The system waits until theimage variation exceeds the threshold, at which time the motiondetection means 806, 896 provides an indication that motion has beendetected in window 2 830. As shown in result block 912, the motiondetection signal means that the contrast medium has now progressed tothe end of the viewing area. Therefore, the method continues at step884, which is the beginning of a sequence of steps in which the systemperforms the operator-programmed radiographic exposure and moves to asubsequent desired examination location.

In step 884, the radiographic exposure is performed. In step 886, thecontrol system 501 determines whether the "stepping" mode has beenselected. If the stepping mode has been selected, the method continuesat step 888. The control system 501 determines whether the currentstepping program has completed. If the stepping program has beencompleted, the method jumps back to step 864 to wait for the operator toinitiate another fluoroscopic examination. If the stepping program hasnot been completed, the method continues in step 890. The imaging systemadvances to the user-selected location associated with next programmedexamination step. This location may be explicitly programmed by theuser, or it may be calculated by the imaging system according touser-selected parameters. The method then jumps back to step 864 to waitfor the operator to initiate the fluoroscopic examination portion of thenext programmed examination step.

If, in step 886, the control system 510 determines that the "stepping"mode was not selected, the method continues at step 892. The controlsystem determines whether the "follow" mode was selected. If the"follow" mode was not selected, then the method jumps back to step 864to wait for the operator to initiate another fluoroscopic examination.However, if the "follow" mode was selected, then step 894 is performed.The control system 510 uses information from the video signal producedby the fluoroscopy system and the motion detection means to continuouslyreposition the digital imaging platform 114 to follow the progression ofthe contrast medium through the patient's body. The control system 510uses servo control techniques to automatically move the digital imagingplatform to maintain the video image variation at the threshold level,thereby maintaining the contrast medium in the center of thefluoroscopic image. As the digital imaging platform 114 follows thecontrast medium, the control system 510 periodically initiatesradiographic exposures. The "Follow" mode terminates upon operatorrequest or when the contrast medium and digital imaging platform havereached the programmed examination zone. When the "Follow" mode isterminated, the method jumps back to step 864 to wait for the operatorto initiate another fluoroscopic examination.

According to an aspect of the present invention, the imaging system 100may analyze a video signal representing an acquired x-ray or opticalimage to detect motion or another significant change in the image. Theresulting motion detection signal may be used to control the operationof the imaging system, providing certain automatic features whichprovide high image quality while advantageously reducing the x-ray dosedelivered to the patient and the operator.

FIG. 7 is a flow chart illustrating a first exemplary method for usewith the inventive imaging system 100 for detecting motion or otherchanges in a stream of video image information, in which the method maybe performed in conjunction with programmable processor components of ageneral-purpose commercially-available image processor. Thus, a suitablegeneral-purpose commercially-available image processor, and the methodof FIG. 7, may be used to implement to motion detection means 496 ofFIG. 2. The result from the motion detection method of FIG. 7 may beused with the methods of FIGS. 4 and 6 to enable the imaging system toprovide certain automatic operations in coordination with the detectedmovement. The image processor may provide a variety of functions inaddition to motion detection.

For simplicity, the following discussion of FIG. 7 assumes that anentire image processor, including any required input or output signalconversion equipment, is dedicated to the motion detection method 920shown therein, for a single video signal. However, one of skill in theart will recognize how an image processor might handle motion detection(or other functions) for multiple signals using well-known multi-taskingtechniques, and how multiple image processors could also be used toservice additional channels.

Although the internal organization of commercially available imageprocessors may vary, the image processing functions are generallyperformed using digital processing techniques. In the discussion below,it is assumed that the image processor has at least the followingfacilities, which are believed to be commonly provided in commercialimage processors: (a) suitable means for converting an input videosignal into digital data representing the amplitude of the signal or theluminance of the image at an array of image locations; (b) means forstoring at least two successive frames of the video signal; (c)processing means, related memory, and input/output having at least thecapabilities of a basic microprocessor-based computer; and (d) theability to generate an output video signal as modified by processing.

The method 920 start in step 922. In step 924, the processor determineswhether the user has selected a "test" mode for setting-up and adjustingwindows of interest in motion detection (see windows 820, 830 of FIG.5), or an operational mode. If the user has selected the test mode, themethod continues with step 926. A first video frame is captured from theinput video signal and digitized. In step 928, the digitized image isstored in a video memory. In step 930, a subset of the memoryrepresenting a portion of the image is defined as a window. In itssimplest form, as shown by window 820 (FIG. 5), the window may berectangular, having left-hand, right-hand, top, and bottom edges 812,814, 816, and 818 respectively. However, other shapes could also beused. In addition, more than one window may be generated (see FIG. 5).

In step 932, the shape of the window is displayed to the user over thedigitized image. Several methods are known in the art for displaying thewindow shape to the user. For example, all of the pixels forming thewindow may be illuminated, the pixels at the window borders may beilluminated, or the window may be highlighted by increasing theluminance of each pixel in the window by a predefined amount.

In step 934, the processor determines whether a window adjustmentrequest, such as a change in the controls of the motion detection userinterface 458, is pending. If a request is pending, then in step 936,the window size, shape, or position is changed accordingly, and in step938, the motion detect threshold level is defined. The method thencontinues in step 940. If, in step 934, no window adjustment request waspending, the method jumps directly to step 940.

In step 940, the processor determines whether the user has requested toexit the set-up mode. If the user has not made such a request, then themethod returns to step 934 to await another window adjustment request.Otherwise, the method continues at step 942.

If, in step 924, the processor determines that the user did not selectthe test or set-up mode, then the method jumps directly to step 942.Step 942 is the first in a sequence of steps in which the actual motiondetection function is performed. In step 942, a first frame of imageinformation is captured and digitized. In step 944, the digitized imageis stored in a first video memory location "A". In step 946, theprocessor establishes a selected characteristic of the image in videomemory location "A" as reference or baseline level for the image in thewindow, against which subsequent frames of video information will becompared in order to detect change. The selected image characteristicmay be, for example, the integrated brightness of that portion of theimage which is within the user-defined window. In step 948, the nextframe of image information is captured and digitized. In step 950, thedigitized image is stored in second video memory location "B".

In step 952, the processor compares the selected charateristics of thetwo images in memory locations "A" and "B," considering only thoseportions of the images within the defined window. The result of thecomparison is a value representing the difference between the twoimages. In step 954, the processor determines whether the imagedifference value produced in the comparison exceed the user-selectedimage variation threshold level. If the image difference value exceedsthe threshold, then step 956 is performed, and the image processorproduces the "motion detected" signal. If the image difference valuedoes not exceed the threshold, then the method jumps to 948 to repeatthe process. A new image is acquired and saved; the comparison with thereference value is performed; and this process is repeated until motionis detected.

FIG. 8 is a block diagram showing the organization of a motion detectioncircuit or module 410 for use in detecting motion or change in a streamof video image information. FIG. 9 is a flow chart illustrating a secondexemplary method 958 for use with the inventive imaging system 100 fordetecting motion or other changes in a stream of video imageinformation, in which the method may be performed in conjunction withthe motion detection system of FIG. 8. The result from either of themotion detection methods of FIGS. 7 or 9 may be used with the methods ofFIGS. 4 and 6 to enable the imaging system to provide certain automaticoperations in coordination with the detected movement.

As best seen in FIG. 8, the motion detection module 410 receives one ormore video signals, such as 412, 414, from optical camera 408 and imageintensifier 166, respectively, by means of an input amplifier 416. Theinput amplifier selects one of the input signals for use, amplifies it,and supplies the selected, amplified output on lead 418 to a black-levelrestoration means 424, a synchronization impulse separator means 420,and an output video amplifier/mixer means 440. The black-levelrestoration means 424 clamps the black level (i.e., theminimum-luminance or baseline level) of the input video signal to astandard reference level. This provides a stable reference for futuresignal processing. The output of the black-level restoration means 424is a restored video signal provided on lead 426 to the window generator428 and to a window integrator 444.

A motion detection user interface 458 allows the user to control thelocation and size of each window of interest (820, 830; FIG. 5) inmotion detection. The motion detection module 410 is shown withcapabilities to process a single video signal at one time, and toconsider motion in a single window. However, the motion detection module410 may be expanded to process multiple video signals simultaneously byduplicating all of the circuitry for each required video signal. Eachmotion detection module may be expanded to consider motion in multiplewindows by duplicating the window generator 428, window integrator 444,sample and hold 450, and window comparator 456 for each required window.The motion detection user interface 458 provides the location and sizeof the window, as specified by the user, to the window adjustmentscontrol 476, over lead 474. For example, the user may use the controlsto specify the vertical and horizontal locations of each of two opposingcorners of the window. Alternatively, the controls 464, 466, 468, and470 may specify the vertical and horizontal position of corner of thewindow, along with the width and height of the window.

The synchronization impulse separator means 420 extracts vertical andhorizontal synchronization pulse information from the amplified videosignal 418. The extracted synchronization information is supplied tocontrol logic 420, sample and hold circuit 450, and window generatormeans 428, via leads 422, 454. The synchronization information allowscomponents of the motion detection module 410 to correlate a position inthe video image with a time offset from the beginning of each frame ofthe video signal. The control logic 430 produces control signals 432which are supplied to a window brightness control means 434.

The window adjustments control provides the location and size of thewindow to the window generator 428 via lead 478. The window generatoruses this information, in conjunction with the synchronization signalsto produce a window borders output signal 442 which indicates when therestored video signal 426 contains image information which is within thewindow. The window generator 428 contains programmable counters. Bycounting the number of horizontal synchronization impulses (orhorizontal lines) from the vertical synchronization impulse (whichrepresents the start of the frame), particular horizontal lines areselected as upper and lower borders of the window. Horizontalsynchronization counters #1 and #2 perform this function. By countingtime from the beginning of the horizontal synchronization impulse,particular positions on the horizontal line are selected as the left andright borders of the window. Time counters #1 and #2 perform thisfunction.

The window integrator 444 receives the restored video signal 426 and thewindow borders signal 442 and performs an integration of the brightnessof the image represented by the video signal, but only when the videosignal contains information which is within the window, as enabled bythe window borders signal 442. Thus, the output signals 446, 448 of thewindow integrator 444 describe the integrated brightness of just thatportion of the video image which is within the window.

The window brightness control means 434 receives a signal 436 from thewindow generator 428 indicating when the video signal represents imageinformation corresponding to locations within the window. The windowbrightness control 434 operates in the set-up mode produces an"additional brightness" signal 438 to the output video amplifier/mixermeans 440, indicating when the video signal corresponds to a locationinside the window. The output video amplifier/mixer means 440 uses theamplified composite video signal 418 and the "additional brightness"signal 438 to produce an output video signal 488 which is supplied tothe video monitor 486. The output video signal 488 is similar to theinput signal, but its brightness is enhanced whenever the "additionalbrightness" signal 438 is enabled. Thus, the portion of the image withinthe window appears brighter than the remainder of the window. When theset-up mode is enabled, this feature allows the user to observe wherethe borders of the window are located, permitting convenient adjustmentthereof.

The sample and hold circuit 450 is responsive to a signal 454 from thesynchronization pulse separator 420. A sample-and-hold circuit 450samples the output signal 446 from the window integrator 444 at thebeginning of each new video frame. Thus, at the end of each video frame,the window integrator output signal 448 presents the window-limitedintegrated brightness of the current video frame, and the sample andhold circuit output signal 452 presents the window-limited integratedbrightness of the previous video frame. Signals 448 and 452 are providedto the window comparator 456. The motion detection user interface 458provides motion detect threshold level, as specified by the operator, tothe window comparator 456. If the difference between signals 448(current frame brightness) and 452 (previous frame brightness) exceedsthe motion detect threshold level selected by the operator, then thewindow comparator asserts the motion detect signal 482.

FIG. 9 is a flow chart illustrating a second exemplary method 958 foruse with the inventive imaging system 100 for detecting motion or otherchanges in a stream of video image information. The method 958 of FIG. 9may be performed in conjunction with the motion detection system 410 ofFIG. 8, or with any other suitable video signal processing means.

The method 958 starts at step 960. In step 962, the input image signalis buffered and amplified. In step 964, the black level of the amplifiedvideo signal is restored to a standard baseline level. In step 966, thevertical and horizontal synchronization pulses are extracted from thevideo signal.

In step 968, a test is made to determine whether the motion detectionmodule 410 is in a test or "set-up" mode, or in the operating mode. Ifthe motion detection module is in the set-up mode, the method continuesin step 970.

In step 970, horizontal line counter #1 is programmed for the linenumber corresponding to the upper border of the window. In step 972,horizontal line counter #2 is programmed for the line numbercorresponding to the lower border of the window. In step 974, timecounter #1 is programmed for the pixel clock value corresponding to theleft border of the window. In step 976, time counter #2 is programmedfor the pixel clock value corresponding to the left border of thewindow. In step 978, the window is displayed or highlighted on theimage. For example, the brightness of the video signal may be increasedwhenever the signal corresponds to image locations within the window.

In step 980, a test is made to determine whether a window adjustmentrequest, such as a change in the controls of the motion detection userinterface 458, is pending. If a request is pending, then in step 982,the window size, shape, or position is changed accordingly, and in step984, the motion detect threshold level is defined. The method thencontinues in step 980. If, in step 980, no window adjustment request waspending, the method jumps directly to step 986.

In step 986, a test is made to determine whether the user has requestedto exit the set-up mode. If the user has not made such a request, thenthe method returns to step 980 to await another window adjustmentrequest. Otherwise, the method continues at step 988.

If, in step 968, it is determined that the motion detection module isnot in the test or set-up mode, then the method jumps directly to step988. In step 988, that portion of the first frame of the video signalwhich is located within the user-selected window is integrated todetermine an integrated window brightness. In step 990, the integratedwindow brightness of the first frame of the video signal is establishedas a reference or baseline level for the image in the window. In step992, that portion of the "next" frame of the video signal which islocated within the user-selected window is integrated to determine anintegrated window brightness.

In step 994, the reference integrated window brightness value determinedfrom the first frame of the video signal is subtracted from theintegrated window brightness value determined from the "next" frame. Theresult represents the difference in window brightness between thereference frame and the next frame. In step 996, the brightnessdifference value is compared with the motion detect threshold leveldefined in step 984. If the difference value exceeds the threshold, thenstep 998 is performed and the motion detection module asserts the"motion detected" signal. However, if the difference value does notexceed the threshold, then the method jumps to 988 to repeat theprocess. Steps 988-996 are repeated on successive frames of the videosignal until motion is detected.

The above-described embodiments of the invention are merely examples ofways in which the invention may be carried out. Other ways may also bepossible, and are within the scope of the following claims defining theinvention.

What is claimed is:
 1. In a diagnostic medical imaging system adaptedfor radiographic and fluoroscopic examinations of a patient, said systembeing capable of operating in a fluoroscopic examination mode at aselected fluoroscopic pulse rate employing frame integration at aselected frame integration rate, and in a radiographic examination mode,comprising:means for producing x-rays directed toward an examinationregion of interest; means for receiving x-rays and producing therefromimage information relating to said examination region of interest; meansfor detecting change in said image information relating to saidexamination region of interest; and means responsive to said means fordetecting change in said image information for causing a change inradiographic or fluoroscope or imaging operating parameters of saidimaging system; the improvement wherein said means for causing a changein radiographic or fluoroscopic or imaging operating parameter of saidimaging system changes said frame integration rate.
 2. In a diagnosticmedical imaging system adapted for radiographic and fluoroscopicexaminations of a patient, said system being capable of operating in afluoroscopic examination mode with edge enhancement at a selected level,and in a radiographic examination mode, comprising:means for producingx-rays directed toward an examination region of interest; means forreceiving x-rays and producing therefrom image information relating tosaid examination region of interest; means for detecting change in saidimage information relating to said examination region of interest; andmeans responsive to said means for detecting change in said imageinformation for causing a change in radiographic or fluoroscopic orimaging operating parameters of said imaging system; the improvementwherein said means for causing a change in radiographic or fluoroscopicor imaging operating parameter of said imaging system changes said edgeenhancement level.
 3. In a diagnostic medical imaging system adapted forradiographic and fluoroscopic examinations of a patient, said systembeing capable of operating in a fluoroscopic examination mode and in aradiographic examination mode, comprising:means for producing x-raysdirected toward an examination region of interest; means for receivingx-rays and producing therefrom image information relating to saidexamination region of interest; means for detecting change in said imageinformation relating to said examination region of interest; meansresponsive to said means for detecting change in said image informationfor causing a change in radiographic or fluoroscopic or imagingoperating parameter of said imaging system; the improvement wherein:said system further comprises means for determining a rate of relativemotion between said patient and said imaging system; and said meansresponsive to said means for detecting change in said image informationfor causing a change in radiographic or fluoroscopic or imagingoperating parameter of said imaging system varies said parameter by anamount related to said rate of relative motion.
 4. In a diagnosticmedical imaging system adapted for radiographic and fluoroscopicexaminations of a patient, said system being capable of operating in afluoroscopic examination mode and in a radiographic examination mode, ofthe kind including:means for producing x-rays directed toward anexamination region of interest; means for receiving x-rays and producingtherefrom image information relating to said examination region ofinterest; means for detecting change in said image information relatingto said examination region of interest; and means responsive to saidmeans for detecting change in said image information for causing achange in radiographic or fluoroscopic or imaging operating parametersof said imaging system; the improvement wherein said means responsive tosaid means for detecting change in said image information for causing achange in radiographic or fluoroscopic or imaging operating parametersof said imaging system varies said radiographic or fluoroscopic orimaging operating parameter by an amount proportional to a rate ofchange of said image information detected by said means for detectingchange.
 5. A diagnostic medical imaging system adapted for radiographicand fluoroscopic examinations of a patient, said system being capable ofoperating in a fluoroscopic examination mode and in a radiographicexamination mode, comprising:means for producing x-rays directed towardan examination region of interest; means for receiving x-rays andproducing therefrom image information relating to said examinationregion of interest; means for storing at least first and second sets offluoroscopic operating parameters; means for deriving movement relatedinformation producing an indication when movement of said patient withrespect to said imaging system, requests for movement of said patientwith respect to said imaging system, or change in a visible feature ofsaid image information occur; and means responsive to said means forderiving movement related information for operating said imaging systemusing said first set of fluoroscopic operating parameters when saidindication is absent and for operating said imaging system using saidsecond set of fluoroscopic operating parameters when said indication ispresent wherein:said second set of fluoroscopic operating parametersincludes a fluoroscopic pulse rate parameter; and said system furthercomprises:means for determining a rate of relative motion between saidpatient and said imaging system; and means for varying said fluoroscopicpulse rate parameter by an amount related to said rate of relativemotion.
 6. A diagnostic medical imaging system adapted for radiographicand fluoroscopic examinations of a patient, said system being capable ofoperating in a fluoroscopic examination mode and in a radiographicexamination mode, comprising:means for producing x-rays directed towardan examination region of interest; means for receiving x-rays andproducing therefrom image information relating to said examinationregion of interest; means for storing at least first and second sets offluoroscopic operating parameters; means for deriving movement relatedinformation producing an indication when movement of said patient withrespect to said imaging system, requests for movement of said patientwith respect to said imaging system, or change in a visible feature ofsaid image information occur: and means responsive to said means forderiving movement related information for operating said imaging systemusing said first set of fluoroscopic operating parameters when saidindication is absent and for operating said imaging system using saidsecond set of fluoroscopic operating parameters when said indication ispresent wherein said means for varying said fluoroscopic pulse rateparameter by an amount related to said rate of relative motion variessaid parameter by an amount proportional to said rate of relativemotion.
 7. In a diagnostic medical imaging system adapted forradiographic and fluoroscopic examinations of a patient, said systembeing capable of operating in a fluoroscopic examination mode and in aradiographic examination mode, including:means for producing x-raysdirected toward an examination region of interest; means for receivingx-rays and producing therefrom image information relating to saidexamination region of interest; means for deriving movement relatedinformation producing an indication when movement of said patient withrespect to said imaging system, requests for movement of said patientwith respect to said imaging system, or change in a visible feature ofsaid image information occur; means responsive to said means forderiving movement related information for operating said imaging systemin said fluoroscopic examination mode whole said indication is absent;and means responsive to said means for deriving movement relatedinformation for performing a radiographic exposure when said indicationis received: the improvement wherein said means for deriving movementrelated information comprises:means for measuring a characteristic ofsaid image information relating to said examination region of interest;digital means for storing, in the form of a digital word, saidcharacteristic corresponding to said image information at an initialtime; digital means for storing, in the form of a digital word, saidcharacteristic corresponding to said image information at a subsequenttime; digital word comparison means for comparing the stored digitalword representing said characteristic determined at an initial time withthe stored digital word representing said characteristic determined at asubsequent time to produce a digital indication of change in said imageinformation; and means responsive to said indication of change in saidimage information for initiating a radiographic exposure when saidindication exceeds a predetermined threshold.
 8. A method for use with adiagnostic medical imaging system adapted for radiographic andfluoroscopic examinations of a patient, said system being capable ofoperating in a fluoroscopic examination mode and in a radiographicexamination mode, said system including means for deriving movementrelated information relating to movement of the patient or the imagingsystem or in an image obtained therefrom; the method comprising thesteps of:(a) establishing a first set of fluoroscopic and imagingoperating parameters for use in non-movement conditions; (b)establishing a second set of fluoroscopic and imaging operatingparameters for use in movement conditions said second set offluoroscopic and imaging operating parameters including an edgeenhancement level greater than that of said first set of fluoroscopicand imaging operating parameters; (c) causing said imaging system toinitiate a fluoroscopic examination according to said first set offluoroscopic and imaging operating parameters; (d) receiving saidmovement related information: and (e) causing said imagine system tooperate according to said second set of fluoroscopic and imagingoperating parameters.
 9. A method for use with a diagnostic medicalimaging system adapted for radiographic and fluoroscopic examinations ofa patient, said system being capable of operating in a fluoroscopicexamination mode and in a radiographic examination mode, said systemincluding means for deriving movement related information relating tomovement of the patient or the imaging system or in an image obtainedtherefrom: the method comprising the steps of:(a) establishing a firstset of fluoroscopic and imaging operating parameters for use innon-movement conditions: (b) establishing a second set of fluoroscopicand imaging operating parameters for use in movement conditions, saidsecond set of fluoroscopic and imaging operating parameters including aframe integration rate smaller than that of said first set offluoroscopic and imaging operating parameters; (c) causing said imagingsystem to initiate a fluoroscopic examination according to said firstset of fluoroscopic and imaging operating parameters; (d) receiving saidmovement related information; and (e) causing said imaging system tooperate according to said second set of fluoroscopic and imagingoperating parameters.
 10. In a diagnostic medical imaging system adaptedfor radiographic and fluoroscopic examinations of a patient, said systembeing capable of operating in a fluoroscopic examination mode and in aradiographic examination mode, including:means for producing x-raysdirected toward an examination region of interest; means for receivingx-rays and producing therefrom image information relating to saidexamination region of interest; means for deriving movement relatedinformation producing an movement of said patient with respect to saidimaging system, requests for movement of said patient with respect tosaid imaging system, or change in a visible feature of said imageinformation occur; means responsive to said means for deriving movementrelated information for operating said is system in said fluoroscopicexamination mode while said indication is absent; and means responsiveto said means for deriving movement related information for performing aradiographic exposure when said indication is received; the improvementcomprising:first image change detection means responsive to image changein a first selected image region for producing a first signal indicatingsaid change; second image change detection means responsive to imagechange in a second selected image region for producing a second signalindicating said change; means for initially causing said imaging systemto operate according to a first set of fluoroscopic and imagingoperating parameters; means responsive to said first signal for causingsaid imaging system to operate according to a second set of fluoroscopicand imaging operating parameters non-identical with said first set; andmeans responsive to said second signal for initiating a radiographicexposure.
 11. In a method for use with a diagnostic medical imagingsystem adapted for radiographic and fluoroscopic examinations of apatient, said system being capable of operating on a fluoroscopicexamination mode and in a radiographic examination mode, said systemhaving means for collecting image information from said patient to forma representation of an image; the method comprising the steps of;(a)establishing fluoroscopic and imaging operating parameters; (b) definingat least one region of said representation of an image; (c) performingthe fluoroscopic examination; (d) detecting image change in at least oneof said defined regions of said representation of an image; and (e)causing said imaging system to initiate a radiographic exposure; theimprovement wherein:step (a) thereof further comprises the step of (a1)defining initial fluoroscopic and imaging examination parameters; step(b) thereof further comprises the step of (b1) defining first and secondregions of said representation of an image; step (c) thereof furthercomprises the steps of:(c1) initiating the fluoroscopic examinationaccording to the initial fluoroscopic and imaging examinationparameters; and (c2) detecting image change in said first defined regionof said representation of an image, and responsive thereto, causing saidimaging system to operate according to adjusted fluoroscopic and imagingexamination parameters; step (d) thereof further comprises the step of(d1) detecting image change in said second defined region of saidrepresentation of an image; and step (e) thereof further comprises thestep of (e1) responsive thereto, causing said imaging system to initiatesaid radiographic exposure.